Is there a possibility I'm pregnant?

My last period started this past Monday and I came off of it on Friday. Yesterday I spent the night with my fiance and for whatever reason I let us mess around without a condom on for a little while. He didn't orgasm and would frequently check to see if he was "leaking" but my paranoia is getting to me. What are the chances that something could have happened last night and I could be pregnant or have conceived?