Planning to make a pulley cover then it dawned on me that I have to take temperature in to consideration.

It is less obvious with coatings, but it is still visible. The only real way to reduce this is to post-cure before coating the part, so that shrinkage is very minimal. Ideally one should always post cure the parts in their mould prior to demoulding so that the mould surface is able to 'balance' the laminate and keep it flat while it cures.