A couple days is not long - the paint isn't cured. m Ransley has the
right idea. Try the denatured alcohol first - I'm sure its cheaper than
Goof Off, though I like Goof Off.

Either way, you'll need a good stiff scrub brush.

tip: If I don't know whether existing paint is latex or oil, I use
denatured alcohol. Denatured alcohol will cut into the latex but not
the oil-based.