i pulled a rib muscle pretty hard while i was surfing a few years back, i did a huge number because it took me about 3 months to recover, it hurt so bad i couldn't take full deep breaths because my chest expanding would hurt so bad.
I was getting to the end of a 3 hour sessions talking with my buds and a huge set rolls in, i'm facing out to sea, i grab my board jerk it around to start paddling and immediate pain, didn't catch the wave cause i was too busy crying =p (not really but it hurt). I'd recommend taking a break until it fully heals, might be hard to do now, but you wouldn't want to risk injuring it more.