zipper aligning

Hi people!, So it's my time to go toe to toe with zippers.

So im designing this wallet. This is the second prototype. Nerly there. So I made a wood block, to put inside the wallet, to align the zipper. But, its still looks kinda bad. So, my new idea, after searching the internet, is to make a block, with a 5mm slit ind the middle, to help me center the zipper.

And here comes my question. Should the block, be 100% same size as the template? or just a little smaller/bigger?

Also, is 1.5cm/3/5 inches thickness of the block standard size or?

Zipper is a little wonky :D