Many people forget to increase on the left side of their knitting when doing the gusset for the Fleegle Heel. All of a sudden you’ve got 19 stitches on one toe-up Fleegle heel and 20 on the other. To fix it, drop your stitch down and re-add the M1. You can do it!
Video: Forgot Increases on Fleegle Heel Gusset