Should I take my birthday off?

So within this summer, I will be working 40 hours a week, 10 weeks this summer at 10 dollars an hour for a gross income of 4000. I already have to take four days off of work for orientation (college) and camp. So, my summer gross income is already down to $3600. My birthday is Monday, July 22. My best friend works this summer too. And he gets Mondays off. So, I can either work that day and make 100 dollars gross income, not forgetting you can do a lot with 85 dollars and I'm going to college. Or I can take my 18th birthday off and spend the Monday off with my best friend. $85 compared to college tuition sounds like a little. And me and my best friend are going separate ways so now I'm faced with the dilemna of taking the day or working that day. Because, if I take the day, not only am I spending money for my birthday but there is the opportunity cost of 100. Anyone has any suggestions?