Make sure the bike you ride fits you; that the seat is properly adjusted. I'd be more worried about screwing up your knees or other joints riding in completely unconditioned form. Also, do like was recommended and try a 10-15 mile ride tomorrow and see what your average speed is and how you feel afterwards.

I did a ~60 mile trip last week with some small hills and an almost full camping load and only had done a 26 mile ride up to that point. It wasn't too bad but i was a bit sore the second day after.