Just like hill climbing, the only way to boost your confidence is to do more of them.

I had a crash on the flats while in a right-hand turn (front blow-out). It took quite a bit of time to get over the crash mentally. It was longer than the physical recovery.

Maybe you could consider finding a hill to practise your descending skills on--one that you've recon'ed ahead of time to ensure that there are no potholes or gravel. Climb the hill, turn around, and bomb back down. Quit while on a good note to re-enforce the positives of the experience.