do you need a heat shield, and if so dose it have to cover my cat?

No you dont need any sheilds to cover the exhaust or the cat for the IVA.

The shields you see on some cars are, for the purposes if IVA, sharp edge covers.

If your exhaust system has the necessary radii on the joints and edges it does not need a cover.

It's always tickled me this one,I failed sva on a plastic reflector not having the correct radius but its fine to have 3 foot of red hot pipe (its now turned a lovely shade of blue through to straw!)down the side of my car that could scar someone especially young toddlers for life.

Thanks for the info