Well first off 50/50 sounds like Waaaay too much. Have you read anything from the first post? It says about the same as water, a little thicker.

Second, did you sand your car first? You have to sand it down a bit at least so the paint will stick.

and as far as just using straight paint, that would take forever to dry. Thats why mineral spirits are needed. It helps thin the paint and helps it flash/dry.

You Need to read more about this. Google $50 rustoleum paint job. should be enough tutorials