You can cut some of the tail off, leave about 3-6", or you can wrap it up into a little bundle. Or redo the cast on using less yarn than you did this time; whatever's left over less 6".
Knitting one row and purling the next causes the edge to curl up. Better to knit about 5 or 6 rows first. Then also knit 5 or 6 sts at the beginning and end of the purl rows to keep the side edges from curling.