As someone who used to paint cars in another life, this looks more like a surface prep problem than a paint problem. Make sure the surface is absolutely clean and rough it up just a bit with some 600 grit sandpaper.
When the paint is dry, make sure to pull the masking tape off properly.
The RIGHT WAY - pull the tape back on itself.
The WRONG WAY - pull the tape straight up off the surface.
I am certainly no expert when it comes to painting models, but I hope this helps.