Ditch the silly fin gluing guides and use double-glue joints... They lock the fins in place on the rocket nearly instantly (about as fast as CA, with none of the low shear strength and brittleness with age CA joints have).
Get an egg carton from the refrigerator (once you've eaten up all the eggs to make the better half happy-- for some reason they don't like eggs rolling around individually in the fridge...) Invert it and slit the egg cups cross-wise from the long-axis of the egg carton, (IE perpendicular) with your hobby knife-- you've now made a handy-dandy fin holding jig for doing double glue joints.
Apply regular yellow wood glue (I prefer Titebond II, but your favorite brand of yellow or white glue will work) to the root edges of the fins in a bead, and spread it evenly across the thickness of the fin... leave it beaded up a little bit (not a HUGE sloppy bead, but not wiped off completely either) and then slide the fin into the slit in the egg cup, and move onto the next fin... do them all at once, and put them in the egg cup slits to dry, root edges up.
Your body tube should have the fin lines on it from the "doorjamb trick" or angle. For extra strength, you can lightly sand the glassine with 220 grit sandpaper along the length of the fin line, where the fin will glue onto the tube. You don't have to sand a bunch-- just rough up the surface some. You should still be able to see the pencil line to align the fin when you're done. Apply a thin layer of yellow glue to the fin lines where the fins will attach, roughly the width of the fin thickness... Set it aside to dry (the valley between the egg cups on the bottom of the egg carton works great to hold the tube while the glue layer dry, making sure the end with the glue applied overhangs the carton, so the tube isn't glued to the carton!)
Give this glue about 20 minutes or so to dry-- the thin layers dry quickly. They can be TACKY, (sticky) but not WET. They can be completely dry-- better dry than too wet!
Apply a fairly thin layer of the same glue to the fin root edge AGAIN a second time, and then carefully align the fin with the fin line on the body tube, and carefully push the fin down against the tube-- ensure the alignment very quickly and that you're holding the fin on straight out from the tube... hold it there for about 15-20 seconds... at this point, the fin should be "locked up" in place and you're ready to go on to the next fin...
If you're REALLY a stickler for perfectly aligned fins, take some scrap balsa (should be some laying around from the kit or various other kits you've built, or you can get a sheet cheap at Hobby Lobby or the hobby shop). Cut a "V" shaped piece, basically an "L" shaped piece about 90 degrees and of equal length on either side of the point... place this across the back of the motor mount or tube and then, using a pair of regular old spring clothespins, clip it to the fins on opposite sides of the rocket (for four finned rockets... this doesn't work for three finned rockets). Then you can go back after say about a half hour to an hour and do the other pair of opposing fins.
I usually apply a LIGHT bead of yellow glue on either side of the fin (to the fillet area) as soon as the fin "locks in place" and then spread that with the tip of my finger very thinly-- this "pre-fillets" the fins, spreading any droplets of glue that might squeeze out from under the fins when you held them in place until they "locked up"... plus it will fill any tiny air pockets that might be in the bead edges from an irregularity... these "pre-fillets" add a lot of strength, and there's not enough glue there to drip, run, or sag-- just enough to spread VERY THINLY over the fillet area-- later you can go back and do all the fillets at one time with Titebond Moulding and Trim Glue, which is thick enough not to drip, sag, or run, and you can do all the fin fillets at once and smooth them with a damp finger, and set the rocket aside to dry-- no muss, no fuss, just beautiful, quick, easy fillets...
If the rocket uses a different number of fins (3, 4, 5, 6, whatever) you can easily cut a cardboard guide by drawing an evenly spaced 3, 4, 5 or whatever shape on a piece of cardboard (usually cereal boxes work quite well for this, but regular cardboard can be used-- just a bit harder to cut.) Make a fin guide by drawing a circle the size of the tube centered over the fin markings (where they intersect) and then cutting out the circle with the hobby knife, and then cutting fin-thickness slots in the cardboard using a steel ruler and hobby knife. This fin guide can be slid over the front or back of the rocket to keep the fins aligned perfectly perpendicular to the surface of the tube and aligned with each other while the glue dries. Tim Van Milligan put a video out of how to make these "fin guides" on youtube IIRC...
Actually, I've never found the fin guides necessary-- I usually use the angled piece of balsa just as insurance... and never had a problem. Works great.
Later and good luck! OL JR
