I'm afraid the damage is done if you rode at all on the crank while it was even slightly loose. I recently learned (also through experience) that cranks are made of relatively soft aluminum, and the tapered spindle on which the crank fits is made of hard steel. The force of your foot deformed the crank, and it won't ever seat again. I got a used left crank, and now my bike has mismatched cranks. It's mildly amusing, and works fine.