Is it my boat or me?

[sv mintaka]

I have a 1979 US 305. It has a lot of windage (not sure if this is the right term but she sits high out of water). I was sailing in about 15 knots of wind on a beam reach and I could not get her to turn downwind (wheel steering). She would turn into the wind but the wind on the hull seemed to keep her going on a beam reach. I tried letting the boom out until the main luffed a bit, still no, so I tried letting the jib out a bit. Still no turning. Am I doing something wrong or is it just the way the boat is? Any and all advice would be great! I have sailed for 8 years and had this boat for the past two. It does not handle anything like my ex-Catalina 27.
Thanks