Crisis! Garter stitch unraveling

I am making a baby blanket that is a series of garter stitch squares, about 4X4 inches each. I am in the process of stitching the squares together and I’m finding that some of them are unraveling. I caught one (see the navy blue square in the attached photo) before I starting sewing it in, but the yellow one started unraveling after I got it almost completely sewed in, and it’s smack dab in the middle of the blanket. I am a pretty experienced knitter, but I’m stumped. In both squares it is the cast off edge that is coming undone. Why is this happening? More importantly, how the heck do I fix it?

Sorry, I had problems attaching the pictures, so here they are:

It could be that you missed a stitch when you were casting off. I’d use a crochet hook to fix it and then secure it with a piece of yarn up at the top. You could put a piece of yarn through the stitch when you get it to the top and then weave in the ends of that piece. Or even sew it down with thread–maybe it would show less than the yarn.

By chance did you cut your tail too short? :shrug:

ETA: I defer to Ingy’s advice :notworthy:

I considered that I might have cut the tail too short with the navy one, as I had to make more squares with that color, but the yellow was the first color I used and I know I wouldn’t have done that with the first batch–I had plenty of yarn.

I hadn’t thought of using thread to secure it–I just may have to do that. I can’t exactly tell how to correct it with the crochet hook though. Should I put the hook through the loop on the right so that I can pull up the loop on the left? Or would I be treating it more like a dropped stitch from the “ladder” below?

I am really hung up on getting this right. I want it to stand the test of time (so far that’s not happening! ) :wall:

Fix it as you would a ladder, but since it’s garter, you’ll have to pull one stitch from the front and the next from the back to maintain the pattern.