if you don't mind, you could use goo gone or something like that....as for the flat black, you could try to use High gloss clear coat to make it shiny, maybe not as shiny as you wanted but, it will give some shine... I got the same thing 2nd time i painted my civic, adhisive and paint bled through the tape... So i masked it up with painter's tape and sanded it down to paint over the again.
Hope you paint job comes out great....
