Beautiful quilt! Such fun, bright colors. =)
I suggest....add a strip of black, then several small 'racing stripes' strips of your brights, then another wide black. The bright stripes could be separated by thin black or all next to each other. This would be a simple way to widen it.
If you wanted to go more complicated...a black strip all around. Then a wider row with miniature/smaller star blocks of the same colors scattered - maybe on point. Maybe 3 small blocks on top/bottom & 5 on the sides. and black corner blocks - with some brightly colored thread for the quilting. =)
Just some ideas to ponder. I'm sure something wonderful will come to you. Have fun with it!
Good Luck!
Donna Mc