Nice looking case. I keep threatening to build one, but haven't gotten to it yet.
Gloss Black Lacquer is one of the hardest finishes to get perfect. Sadly, it doesn't hide flaws, it accentuates them. So, every pore, divot, nook and crannie needs to be filled. Then sanded, then primed, then more sanding until it's smooth as silk, then you can paint, then sand, then paint, then polish.
You might be able to sand what you have level and get an even coat with decent gloss, but I don't think you're going to get gloss like a piano with anything acrylic.