Casting on within a piece

Hi everyone,
I am working on this hat pattern and have come to a part where I have to cast on three stitches on both ends of a row.

Here are the specific instructions. The hat is worked in k2 p2 rib.
Next Row [RS]: CO 3 sts, work new sts in patt and cont in patt to end, CO 3 sts.

I’m not sure what kind of cast on to use here. I tried knitting on the extra 6 stitches but I’m left with a funny looking hole right where I started casting on. Any tips or ideas? Thanks much!

The Backward Loop is good for this kind of thing. So you’d cast on the 3 where your working yarn is, knit across those and the other stitches that are there, and then cast on 3 more.