Bummer. It's always a good idea to wash resin based parts before painting. Depending on how bad it is, you could just sand the offending areas with light sandpaper, then repaint and blend it back in. Without a pic, I can't really tell...
IMHO...it might be better to sand it down totally, then hit it with some Krylon primer. Let it dry for about 24 hours, then hit it with some Flat or Satin Black Krylon paint. I do this for all my blasters and it turns out really well. This is my Hasbro mod E-11 and I used Krylon Primer and Flat Black...then Metallic for weathering.