was this knit in the round? or flat?
(please say round)
anyway heres a trick for ripping out, before you undo your cast on take a tapestry needle and a long cord of floss and thread it through one row of stitches (do not go up and down rows!!!! stay within one band of "v's")
this way when you rip back to that row, the floss will hold your stitches in place and you can put them back on the needle and continue to rib)