I highly doubt you have a fractured penis just from underwear elastic hitting your erection. Uou're probably just overly worried about this, and worry or anxiety can interfere with erectile function. Just relax & I'm sure very soon you will have a normal erection again. If for some reason this issue doesn't clear up on its own, then see a Dr, if your regular Dr cant help, then see a Urologist. But I doubt you'll need to take it that far.