Most Helpful Guy
Make sure he knows that you really were busy. and that you were so sorry about not being able to go out with him. The only thing you might do with the next person if you are busy but interested is to tell him that you are interested but busy and would like to find a good time to meet. But for this situation you just apologize for being busy and if he suggests a time when you aren't working change your other plans. Just be honest with him about how you feel now and it should all work out.