You got it fitted finally, that's the main thing.
: That was always No.1 priority when we moved house, a few times, fit the moggies door!
You are correct regarding the template. First action, BIN-IT!
: Next, Measure up, and using a piece of thin cardboard, make one using the impression method, rather like making a cardboard gasket for a carburettor flange.
Consolation is in making yourself a hand written set of instructions for the next time around. They are stupid things to fit, and if someone says they are easy, could that fellow please replace my cherished Jaguars top, and bottom timing chains and tensioners? Better still, you do the cat-flap mate, I'll sort the Jag! Many Thanks.