If your rocket is 77" long total (6ft 5"), a 3m (13ft) long shock cord may be a problem.
I like to go with 3:1 on shock cord to length of rocket. Now I am starting Dual Deploy, I am still sticking to that. So EACH shock cord in my 6ft rocket is a minimum of 18ft long. I usually have added a few extra yards just for comfort.
with my 21ft comment for your rocket, I was going on 3 * 6.5ft = 19.5ft then throw in a little extra to allow for knots, loops, etc. = 21ft. That would be approaching the minimum length I would be comfortable with, and I am currently using tubular nylon, not Kevlar as you stated. Tubular nylon has some stretch in it, Kevlar does not. When tubular nylon reaches its normal length and keeps going, it will stretch and soak up a lot of the energy of deployment. If kevlar gets to its end and there is still energy in the deployment, it will be taken up (hopefully) by either the daisychain, taped loops, chute deployment, etc. If the energy does not get soaked up somehow, there will be a failure somewhere. Could be a zipper into the airframe, kevlar is nice for doing that; or one of the attachment points will give. If you have done a good job with the epoxy on the motor mount, and you are using 'open' eye bolts, I am pretty sure that they will 'give' before the motor mount does. Coz the kevlar aint gonna snap.