I made peanut butter fudge for the firsts time and it was very good. But I thought seemed a little dry. What would make it dry

Did you use natural pb or Skippy/Jif variety? I find that natural peanut butter tends to yield drier end-products, perhaps because it lacks the hydrogenated oil that Skippy and Jif have.

There are a few things that can result in a dry fudge. One is that you did not dissolve the sugar completely, or you formed crystals in the boiling process. You may also have overcooked the mixture, either for too long or at too high a temperature. It might be possible to recover the current batch somewhat. You could try sealing it in a zip-lock baggie with a damp paper towel overnight to allow it to absorb some moisture. And you could also try re-melting it with a little cream or milk, bringing it up to the correct temperature and re-pouring it to firm up. Though you could also opt to add enough milk to make a fairly smooth sauce as well, and use it that way over plain cake.