Did you miss some of the yo's? Â Or are you possibly accidentally passing both the slipped stitch and the yo over, instead of just the slipped stitch? Â You will pass the slipped stitch over the k1 and the yo, but both the k1 and the yo should remain on the needle.
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Yes, you will have to undo that round, but if you had the right amount of stitches after round 2 of the lace pattern, you don't have to rip the whole thing.  Undoing just one round can be hard for a beginner though.  Do you have a yarn shop nearby where you could find someone to help you fix the mistake?  It is much easier to help with knitting in person, where I can demonstrate and watch.
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