First of all, get that loaded cartridge out of the magazine and put it somewhere where the gun isn't! Remove any loaded ammunition from your work area, and put it in a drawer or other secure and inclosed space.
Next: Can you retract the slide when the UNLOADED magazine is inserted into the pistol?
Last but not least: How far did you disassemble the pistol? Did you just field strip it, or did you remove any internal parts in the frame - in particular the hammer?
