I just went and brought my authentic Coach Bag. that I got from a Coach Store. and I will say that if it IS a fake, it is a perfect one....my C's look identical to those on your bag, and on the zipper as you are showing above I also have the YKK...My shoulder strap stitching is a little different, but that could just be a style thing....Mine is a "bucket" purse...mine is lined in a bluish fabric and does NOT have that big leather square in it.
I think it is highly likely yours is authentic and you got the buy of the century....
If you want to be totally sure, take it to a Coach Store, and they can authenticate it.