I would also trim it down to the smallest measurement. Your pinwheels are more than 1/4" from the edge, so you won't be cutting off any points and you can make it perfectly square. I think it's a cleaner solution than easing the borders in and your quilt will lay flat.
Very cute top!

I was always taught to measure each side and put the exact border measurement on each side. That way the quilt will lay flat. You can play a little bit with less then an inch difference but over that amount you will have a little mound of the quilt in the corner when the borders come in tighter than the quilt. I quilted for those who just sewed any length of fabric on the quilt and it was difficult trying to get all that excess fabric to lay flat. But the opposite also occurs and if you try to average too much, your borders will bow into the quilt. So much I learned when quilting for others. You could trim you quilt if you wanted it to be perfect. The blocks are floating enough with a little room to trim without it showing.

I do not measure the very edge of a quiilt - especially if it is made up of many pieces - because sometimes it gets distorted a bit with a lot of handling. Because at times I am a member of the OCD group, I do take three measurements and average them. One in the center, one a foot or so from the left edge, and another measurement a foot or so from the right edge.

I like the turquoise color you have chosen for the inner border. It enhances the brightness and cheeriness of the center.

Thank you, everyone, for your comments. I have learned a lot.