I didn’t prime my steel exterior door because it was already primed. But the exterior semi-gloss enamel paint didn’t adhere and looks terrible. What should I do to fix it, please help!!!
Often it takes time for paint to fully adhere to a surface. It could be just giving the paint that time. To reduce the chance of sticking remove the weather stripping from the door frame for a day or two.
"Looks terrible", you need to be a bit more specific. Did you brush on the paint and have thick brush marks? It is possible to hide some brush marks by applying another coat with a weenie roller. If the look is too much for this method then you will have to sand off or strip the paint you applied, prime then repaint. Unfortunately there is no easy fix for this.