Sorry if I was technical, did not mean to be.

You can reduce the amount of weather helm by raking the mast forward a bit. It depends on how much you can adjust your standing rigging tough. If you overdo it, you can get other problems, but that's the easiest 'quick fix' for weather helm due to a to large mainsail.

With your amount of initative (chopping the head of an old mainsail, not a thing most sailors would think of or implement in real life), I am sure you will be a great sailor. Get Rick's book "Catamaran Racing for the 90's" available in the onlinemarinestore.com section of this site. That book will help you avoid most mistakes you inevitabely will do by the "seat of my pants" approach.

PS: You do know how to, and are able to, right your boat after a capsize? (I always ask this if somebody are new to the game)