Love the colors!!

Beautiful quilt. I made a similar quilt that was too small for our queen bed and since I had plenty of fabric, I just kept going, making more blocks. It's really lovely now. Also I added two borders, one narrow and the last much bigger. I have a long arm too and have hesitated about ruining a quilt. Maybe you need to practice more before you quilt this?

I guess I would add two borders. Both narrower on the sides and much wider at top and bottom to achieve what you want. Having two of them would make the changes less noticeable. (A little. LOL)