I agree with many of the other suggestions you've received but here's my suggestion.
First, fold under your unfinished edges of the quilt to give you a square/rectangle without the uneven edges. Then, start with madquilter's suggestions as to color/proportion. You say you have lots of red in your stash.
Fold your red into the 2" width and lay next to your quilt. If you have a FQ of blue and/or white - fold that to the 4" / 6" widths and lay those next to the red. Play with those colors/proportions. Take photos. Then, play with the color placement. Take more photos. Then, play with with proportions/colors in different positions. Take more photos. You will not remember which you like best without having the photos side by side.
You might like a 1"; 3" 6" or 9" variation. Play with it for a while. If you have enough fabric, fold it and place it on both edges of the corner to get a better view. It could be mitered or not. Just go for color/placement/proportion at this point. Study each or a bit. It will speak to you.
As another poster mentioned - there are no quilt police. Do what is pleasing to you.