I can think of one thing that may have happened--it wouldn't be obvious if you're working knit-the-knits and purl-the-purl ribbing.
When you work with circulars, you should always be knitting on the outside of the tube. The needles are closest to you and the cable is away--think of sipping out of a tea cup and the rim is your needle.
What often happens is that you start to knit on the inside of the tube rather than the outside. This becomes obvious when you're working in stockinette, but with ribbing, you adjust your stitches.
I'd tink (unknit) back to get rid of the part with three rows. AT the end of that section, (which will be obvious when you get to it) turn your needles so you're working on the outside and you should complete the second round and come out even.