The private pilot had just refueled his single-engine experimental airplane in preparation for the next leg of his cross-country flight. During lift-off, the pilot reported that the right wing felt heavy and the airplane was veering to the right. He applied left rudder, reduced power, lowered the nose, and landed hard. Subsequently, the left main gear and nose gear collapsed and the airplane went of the left side of the runway. The pilot reported that he failed to properly secure the large fuel panel located on the top of the right wing. In addition, he reported there were no mechanical deficiencies with the airplane or the engine.