feeling anxious

Good morning to all.  Today I get to volunteer at the humane society this afternoon but I'm  having like a panic attack or something.  I feel like I want to stay in the house and not go anywhere. I hate feeling like this.  I was really looking forward to  this but now I find that I'm trying  to talk myself out of going.  The closer to the time, the more anxious I get.  Does anyone have any advice how to chill out and enjoy my volunteer time like I want to?