Well, first bit of advice, ALWAYS hold the mainsheet in your hand while sailing, use the camcleat to hold the tension, but ALWAYS hold the mainsheet tail in your hand while sailing, that way when a gust hits you can instantly release the sheet ot spill the wind before you tip far enough to take water over the lee rail.
If it is windy, try sailing with out the jib, just raise the CB a bit to reduce the weather helm created by the moving of the sail area aft.
I'm confused by your description of the problem though, you say yo uhave a strong weather helm, but them mention that yo ucan't get the boat to round up into the wind? Did you mean to say that you have a strong LEE HELM? Weather Helm is the tendancy for the boat to turn into the wind if you let go of the tiller and a slight amount of weather helm is desirable for that reason. Lee Helm is the tendency for the boat to turn AWAY from the wind (bow turns away from wind if you let go of tiller). Either tendancy can be adjusted by raking hte mast (lean mast back to increase weather helm, lean mast forward to reduce weather helm. Obviously, reducing weather helm will increae lee helm, so you do not want the mast to rake forward, but instead slightly aft) Balance (lee vs weather helm) can also be adjusted by raising or lowering the centerboard. Raising the board slightly will reduce weather helm, lowering the Cb will increase weather helm. Condition of the sails can effect weather helm, old worn-out sails tend to cause more weather helm and will actually increase the heeling as well. Newer sails will provide more driving power with less heeling, older sails may be able to be flatened a bit by making the outhaul, down haul and main halyard tighter.
