sailing in circles! please help
It sounds like lee helm, a tendency for a boat to fall off to leeward, which can be dangerous. Weather helm, the tendency to round up into the wind, is safer because when the tiller is unattended, the boat will stall out by pointing into the wind. With lee helm, the boat will accelerate as it falls off the wind.
Does your boat have a centerboard? If it does, you may need to lower it fully when going to windward to have more control over the helm. The oversized jib could be contributing to the problem. Can you reduce it by reefing or rolling it up (if a roller furling jib)? If not, try sailing under mainsail alone.
Suggest you speak with the former owner, the boat manufacturer, or someone with the same boat or a Dufour 24 to see what they say, and if possible, get someone with experience with the boat to come out for a sail with you.