Howdy!
Get a new set that's got a wider opening for your heel. It's really the best solution. I determined the heel opening size I needed to be comfortable, and before I purchase a set nowadays, I always make sure I get the heel opening size measurement, so I know they'll fit. (Yes, spurs come in various heel size openings; most sellers of quality spurs will be able to give you the measurement of a pair you're looking at.)
As for opening the spurs you have, best plan would be to send them to a professional spur maker and have him try to open them up so the shanks stay straight. This is will entail cost. I don't know how much your spurs are worth so can't say if this is something worth doing.