Now might be the time to get a can of black spray paint and just go round the edges to get a solid black to hide the remaining glue lines. Spray from the inside of the guitar to the edge , never from the edge to the inside, so that you can start spraying high then just bring it down until the edge of the spray just touches the edge of the guitar, then move it along the edge at that angle. It often helps if you can rotate the guitar when doing this rather then move yourself. Putting it on a piece of cardboard (a bit smaller than the guitar) and putting that on another larger piece of cardboard can work well as a makeshift turntable.

I'd still try looking for some glue or adhesive remover as that centre line could look better than it does. In the UK I can get Goof Off, Goo Gone and Evo Stick adhesive removers (and I think Sticky Stuff Remover would probably work as well). It's just a question of using the right search phrase.