You can kind of slip your stitches from one needle to the other to get to where these have crossed and try to uncross them. Just put your needle in as if to purl but don't wrap the yarn.
More likely, though, since you have such vast experience
you kind of knitted into the stitch below, or didn't slide your stitch off correctly.
I would slip like I said above, and see if you can try to get it to look like the others. Count your stitches, too. If you have the right number, counting this X as one, you probably just didn't slip it off the needle correctly. Then slip the stitches back and you should be set to go.