Border length Way off.
 

I measured my quilt through the middle and cut my borders accordingly and they are Wayy too short. At least 1 1/2" too short on both sides. It is just a baby quilt.

Do I attempt to ease that much in? How did I go so wrong on Both sides?

I could piece a little bit to each one I suppose, but it will look silly.

Watson

Can you put blocks in all four corners of the border? Even if they have to overlap the quilt edge, that might work.

How 'bout piecing in a little bit around all 4 corners in a coordinating fabric so it looks sort of like like the old photo-mounting corners (if you're old enough to remember those (-: ). Then it would become a design element...

Cut the borders in half and put a coordinating piece of fabric between each half of the border. It'll look like you meant to do it.

1.5 inches is too much to ease in. When the quilt is washed the border will shrink and the quilt will take on a shallow bowl shape. Ask me how I know...

The technique that I use for border measurement is measure thru the middle and both ends, then average the 3 measurements.
I also agree that 1.5 inches on a baby quilt is a bit too much. I would cut the border in half and add a contrasting strip of fabric.

Take a good look at the blocks in the quilt. It might be a case of a few of the blocks being cut a little 'off'--not quite square. 1 1/2 inches is a lot of difference in a baby quilt. I think I would lay it out and go over the whole thing with a ruler, checking to see where the problem originated, before doing anything with the borders.

Easiest for me would be to do the cornerstones. It could be a design extension from the quilt.

I would rip out seams at least 1/3 in and add another color rectangle. one must measure, cut and pin center, ends and in between. you will get better.

I would figure out why it is so "off" and see if it can be fixed. If not, pieced or cornerstones. Piecing usually disappears once it is all quilted.