I am not a fan of borders added to make the quilt bigger. It looks like borders added to make the quilt bigger. Having only 3 inches of extra backing is taking a risk. I would use a bigger backing even if no borders were being added.

Thank you all for the ideas. I think I'll go borderless. Have lots of length in my backing. I prefer my baby quilts to have a seamless back. My backing is a print of building blocks so it will almost be a reversible quilt.

Not every quilt requires a border. Do what looks good to you. It isn't that hard to add a little to the back if you think the top needs to be bigger. In fact, you can cut your backing fabric in half lengthwise and add a striip of a contrasting fabric there for a very nice look.

I don't always put borders on my quilts but when I do, I usually put a pieced cornerstone in each corner.

Modern quilts are showing no borders and I think they are awesome. The binding will finish your quilt nicely.

I almost never use borders. My mother didn't and neither did my grandmother. Think it's an inherited trait or just what I'm used to? I do a lot of string quilts and make up my pattern as I go so if I want a larger quilt I just make more blocks/rows.

It doesn't take borders to "finish" a quilt. Lots of quilts look better without them, IMO. Hard to say on yours tho, since you didn't show us a picture of it. Just look at the quilt top and imagine it with just a binding on. If it looks ok, then I'd skip the borders. I usually prefer the more "edge to edge" design in my quilts, without borders.