Check to be sure the print is at the correct size. The length of the shroud I printed is right at 9" long.
I mentioned I built mine using a ST-7 tube, what was used in the Centuri kit. (The ST-7 is a little larger diameter over the BT-20.)
The ST-7 wouldn't go all the way forward to the small end of the body shroud. It was about 1/8" short. I trimmed the shroud by 1/8" and it ended up flush with the end of the shroud.
At least on my print, a BT-20 would have been just about right, without trimming down the shroud end.