Casting on in the middle?

Hi there, I am making a pair of mitts in the round and when I put the stitches for the thumb aside it tells me to CO 3 sts, I did that I knit it like it says and I get this strand of yarn under the CO sts, anyone know why this has happened and how I can prevent it?
Thanks

Sandy

How did you do the cast on? If you cast on with the working yarn there shouldn’t be a thread underneath.

You can either do a backwards loop cast on onto the right hand needle or you can do a knitted or cable cast on onto the right hand needle. This will prevent the long strand of yarn behind your work. For the knitted or cable cast on, when you come to the space to cast on, put the right hand needle into your left hand, cast on the stitches and then return the needle to your right hand and continue knitting. There are videos of all these cast ons under the Free Videos tab at the top of the page, Cast Ons. Good luck with the mittens!

You would cast on to the needle where the working yarn is. Either do a loop on that needle, or switch it to the L hand and knit the 3 sts on, then move the needle back to R hand.

You don’t CO to the L needle with the yarn still in the R hand.