Have to work on a freinds birthday party which she really wants me to be there what should i do?

One of my really good friends is having a birthday celebration in a few weeks and would be disappointed if i never came, the problem is I am supposed to work that day, Ive tried getting out of working but it looks as if I’m going to have to work my shift, what should i do? Should i go to work and tell her I’m really sorry?