For a repair like that there are several good products to use, Problem Plastic Adhesive and SMC Repair. Both can be used with a fabric mesh or fiberglass mat for additional strength. one of the most important steps is to V-groove the crack out entirely, which you have done, and grind and feather all paint away from the repair for good adhesion. Looks like you are using a glazing putty without a hardener. Definitely not recommended. That's more for very small imperfections. A two part glazing putty is superior as it will not shrink and adds a small measure of strength to the repair. Good luck with your repair.