Okay, all I can tell you is what I would do...and I was a seamstress for 48 years before I started quilting 4 years ago. I have never used minky fabric and I have never used a serger, though my sister has one that she loves.
If I was trying to put this quilt together, I would trim each column as well as I could. I wouldn't worry if each column was the same width as all the others. I just wouldn't. Just make each column straight on each side, with right angles at the top and bottom of each column.Then I would forget using the serger and sew the columns together with a 1/4 inch seam....(that was the hardest thing for this old seamstress to learn!!!) If the squares aren't all the same size, it won't really matter. No one will care.
I can't tell how large your squares are, maybe four inches??? I am trying to visualize this, but I think I would add two borders...a small inner one and a larger outer one....maybe an inch and a half and then five inches, or maybe four. I would use the darkest fabric as the outer border and then a lighter fabric as the inner border. I would try to use fabric in my borders that matched fabric in the squares. (Experiment laying different fabric beside your quilt to decide what you like best for the borders.)
The fox fabric is so cute. This will be a great baby quilt, even though it may not end up being exactly what you had intended. That isn't uncommon. Many of my quilts have ended up way different than I thought they would, including the one I am just finishing now.
If you can't figure out how to do something....like actually quilting it or adding borders or something, simply google it. You will find answers to any question that way....or ask this group. It is a very helpful group. Without them, I wouldn't have even been able to change the blade in my rotary cutter the first time!
Good luck. You can make this work, and if none of what I have suggested sounds like what you want to do, that is okay too. That is what is great about quilting....it is your quilt, you can do whatever you want with it.
Dina