You should pull the lock strip back out and push it in as you install it (take the stretch out) I've done this in the past and cut the excess off. Use silicone spray on the lock strip and it's easy to force into the groove and take the stretch out.
Yep, There is a tool for inserting the lock strip that helps prevent the stretching. If you were to cut away the excess now the lock will be that much short once it settles.