Without seeing you on the bike, it's hard to give a definitive answer on whether your bike is the right size, but given what I know Cannondales and you being 5'9", my guess is that yes, a 52 is too small.

The big issue is the short headtube, which will have you bending over a lot more than a 54 or maybe even a 56. For a 52, you're looking at 12 cm vs. 14 on a 54. There are a few cheap options to make the head tube taller, including going with a higher degree stem (17 percent) flipped up, or a steertube extender. You may want to try one of those options first. eBay is a great place to find cheap stems to try out new fits.

But if you do want a larger frame, particularly a 56, PM me. I know a guy selling a brand new 56 Caad 10 frame. He'll give you a smoking deal.