Sounds like the guide rod was off center when you reassembled. It's actually fairly common on the P-series, so I have found.
If that is the case, and you can't bring the slide forward, the ejector is probably back in the "up" position. Reach through the mag-well with a dental pick or bent hanger/wire to pull it back down. The slide should come free and slide forward.
Did the ejector pop up when you reassembled it??
If so, reach up into the mag well and pull it down/remove the slide and make sure it's down all the way. Reassembl,e being careful the d@mn ejector don't pop up again! :mrgreen: