steer straight ahead, no turn at all, and put it in reverse. You may have hit a rock or something just big enough to get stuck.
the access ladder to get back on is in the back. eat a stam food and swim around it, see if you see anything or can push on it etc.
you can try waiting on the wind to get behind it and go full sail too, that can break loose.
If nothing works and you can't figure it out, take off your weapon and punch the mast a couple of times. It will do a little damage to the craft but it may shake it loose.

you can try reloading your auto-save backup.

if you must, make a new server, log in and throw your gear into a couple of quick chests, log out, back to the raft and then go die... repop and recover gear. Or use a hack to do so.