You probably knit one sleeve two rows instead of doing one row on each sleeve. I used to do this all the time. I now put a stitch marker between the stitches so I don't just automatically turn and knit the same sleeve again.
I'd unknit back to where both sleeves look right and the yarn is in the right place to start the next row on both sleeves. Try the stitch marker, too, it really helps.
"Trust the pattern!"
Time flies like an arrow, but fruit flies like a banana.
Hop aboard while we follow the cloud-covered van of knitting harmony, man!! Woooo!! --Hedgehog
IngridKH on Ravelry