Firstly, it's always beter to get a bike that's too small than one too big. There is much less pain riding a smaller bike.

One thing you really need to do is try out more bikes. Cannondale are nice, but different brands and models will have different choice sizes and geometry that may be more or less comfortable to your particular body. Trying more bikes will also give you a much better idea of what you should expect out of the fit and comfort. You could make an aim to try a brand that makes a bike around a 53.

Oh and you also need to ride it more than just around the parking lot a few times.