Scarf sides are curling in, not stockinette

Ok, this may already have been answered here, but I’m making a scarf. I purl eight, knit eight, and purl eight, and then every sixth row, I cable the knit stitches. I’m a newb. Anywho, my purled sides keep rolling inwards towards the cable. Is there anything that I can do to it now to fix the rolling, or do I have to start over and do something like: 3 knit, then 8 p, 8 kn, 8 p, and then 3 knit? Your help would be great!

The 8 purled sts are the same as stockinette if you knit on the other side. You need a border on the edges for this too, and maybe 4 sts instead of 3 in garter.