It could be a couple of things. First off, check to see that you have the same number of stitches on your needles that you started with. With seed stich, or any kind of ribbing where you have to switch back and forth, its not difficult to get mixed up and have your yarn on the wrong side of your knitting and end up making a yarn over, thus ending up with an extra stitch and an eyelet.
If that's not the case, it could just be that your tension is a little off now and then, which can happen when you switch from k to p and vice versa.
If you've been making eyelets, you can't really correct it without tearing out to that point. You can either call it a design element
, or if it really bothers you you can kind of stitch it closed when you're done.
If its a tension problem, you can kind of pull and stretch that area and see if you can make it better. Or if you plan on blocking the blanket, it could rectify itself then.
My bet is on the first, if the hole is that noticeable.