How bad did I #$&% my piston up?

Alright...so how exactly does the piston to wall clearance come into effect and what do I need to do regarding that? I apologize if I seem daft on this subject. Or is that something that the machine shop should have taken care of when they had the block/pistons?

So I WILL need to use a file to file down the edges a little bit and just keep doing a trial and error fit until I hit .0026" right?
yes take your time with small bits then recheck.some use a dremel with a disk and lightly squeeze the ring into it.But make sure its .026 not .0026 as you posted.