There *may* be a way to resolve this problem
The fundamental problem is that the "rounding up" forces exterted on the sail overpower the opposing directional forces set by the rudder and keel. In short, you've got a real bad case of "weather helm" and the twin bilge keel design (particularly when sailing upwind and only one of the two keel is providing directional stability) would seem to make the problem worse. While I don't know the set up of your rig, I would think that the following adjustments would reduce the boat's tendency to round up:1. First of all (perhaps most important of all) you need to better "balance" the boat's *combined* center of effort. Weather helm is caused when the *combined* center of effort (i.e. the center of effort between the jib and mainsail) is too far aft of the boat's "pivot point" (i.e. center of lateral resistance). In short, you need to move the combined center of effort FORWARD. To do this, you must reduce the power of the mainsail and increase the power of the jib. 2. To depower the mainsail, increase tension on the outhaul, main halyard, cunningham and boom vang. The point is to reduce the amount of draft depth or "belly" in the main by making the sail as progressively flat as possible. A flat sail does not generate as much lift and hence is less powerful than a full bellied sail.3. Next I would power up the jib by moving the jibsheet fairleads far forward to give the jib greater draft depth.4. When a gust appears to approach, I would be ready to further de-power the mainsail, by allowing the traveler to drop to leeward, decreasing the mainsail's "angle of attack" to the apparent wind. If dropping the traveler is not sufficient, further de-power the mainsail by letting out the mainsheet, but make sure to maintain tension on the boomvang so the sail remains relatively flat.Hopefully, these suggestions will give you more tools to help control the demon of "weather helm". If you've tried these tools, and your still not able to balance the rig fore and aft, you'll need to take more drastic measures such as reefing the main much earlier to more substantially reduce the sail area aft of the "pivot point" of the boat. Additionally, you might want to consider going to a rigger to see if the forestay and backstay are properly tensioned. Food for thought.