Couldn't get the gasget straight

I took the whole inner door liner off the door. I then put the new gasket onto the fiberglass shell . Then I tried to keep it straight, but screws where hard to start. Then get the whole thing back onto the door was entirely a pain !. And when I did, it came out from behind the fiberglass shell. I tried to glue it down ,but the silicon I used was messy. I still have gaps by the the hinges. I think next I will have a repair man do it! !!!! can you give me some hints on how to do it!????