<human>: Can you give me a shortened version of the text?

I'm working a one-week security gig at a certain large music festival in Tennessee right now. Training was a few months ago, and we were asked our shift preference, days or nights, both 12 hour shifts from 8 to 8. All of my friends who are also working here chose days, as did I and my boyfriend. Fast forward a week before we leave, we receive an email from one of the management saying a bunch of night shifters dropped out and weren't going, So volunteers were needed to switch to nights. Being the nice people we are, boyfriend and I decided to offer ourselves over, ON THE CONDITION THAT we would have Saturday night off to see a few of our favorite bands. One of these bands we had tickets for three nights in a row this past spring, and all three shows were cancelled (one of the members had a medical emergency). We were emailed back and told this condition would be verified with the person in charge of scheduling before we were switched to nights. Fast forward to today, Saturday. We were told this morning we have a 50/50 chance of working tonight, but can't find out until 7 PM. If we are scheduled to work, the current plan is to remind them of the agreement, tell them we won't work tonight, and go see our shows anyway. At training, we had to sign an agreement that any shift missed will result in $200 docked from our pay. If this occurs, based on our email communication and an agreement being broken, do we have the legal basis to sue? I'm not overall worried if we're not, considering the things they've provided for us here (transportation, food, free admission, etc) are well worth more than $200. However, I'd like to be able to inform them that suing them for my $200 back is possible, if it is. $200 doesn't seem like much to get worked up about, but I'd like to demonstrate that the college-age kids they enslave for this event each year aren't THAT dumb.
<bot>: Made an agreement with employers that we would work all but Saturday night, might be scheduled anyway, could lose $200 over this, want to know if we can threaten legal action.