Jake,
I have a tendency to really tighten the nut on glow engines. I have never had a problem with a bad one. I don't think the prop nut was the problem. Most often a beginner will flood an engine which will make it backfire and loosen the prop nut. As you continue to try starting the engine it becomes looser. Make sure it is tight and continue to check. Electric starters sometimes make things worse. Get help from an experienced modeler.
Good luck,
EXCAP232