Been there, done that, and survived. It'll get better if you keep going.
First off, don't think so much about the job. Just go get it. It's not going to be nearly as bad as you're anticipating. And if it is, you only have to stick with it 'til you find something better.
As for feeling overwhelmed, I'd set aside two or three days before you begin work to implement the "Getting Things Done" method by David Allen (Google it!). You will feel 100% better by the second or third day, as you'll know exactly what you've been putting off, what you can keep putting off, and what you can't.
Don't forget to relax. You have a master's now, so you're in a better position than the greater majority of the world's population. I'm sure whatever you do, you'll be just fine.
Good luck!