Concrete slab not square - advice please!

I'm having a small 18' x 14' garage built and the 6" concrete pour is not square. The X measurement is, 9 3/4 " out. For it to be squared up by trimming I'd be loosing 7" and that just isn't going to work. I'm meeting the GC tomorrow and he's been a little slippery so far, and I don't want to end up with something I'm not happy with. Whats the best solution? Can they trim it up and then extend by pouring more concrete or will that compromise the whole pour? If it won't, how much should they trim it back? I read on another forum that you need at lease 24" for it to be stable, and then it would need more support than the rest of the pour (which has some mesh) to make sure there are no issues down the line. Any advice would be appreciated!