You've got a really nice quilt .... crisp, clean and fresh look to it.
Do you have to make it bigger? You could stay where you are.
What do you have left in your grab bag? Some thoughts ... join the strips together and then cut like piano keys for the narrow border. Then some more white and then likewise for the outer larger border but with larger pieces.
If you're using fabric from your stash, use some of the grab bag fabrics and make the same strip blocks to put on the corner s of the borders, to tie the inner and outer together.
And then bind it all off with a scrappy binding made with more of the grab bag fabrics.