Crap, messed up a shoulder 3 days before my first Nationals

I'm in Las Vegas for a couple of days and swam with the Las Vegas Masters. For some reason, at 6:00 AM, the age group team sharing the pool changed the lane lines from LC to SC. Shortly after that, were were doing a few slow 50's of backstroke (which was my first mistake - attempting backstroke). I had not noticed there were flags only on one side. Since I am usually successful at avoiding backstroke, I have no clue what my stroke count might be. Just around the time I started getting curious about when I might see the flags, my left arm jammed the wall almost fully extended. Now I have a flash of sharp pain even on slow free every time my hand passes shoulder level.:bitching: I was sensible enough to get out eventually ice it.