Ripple Stitch Pattern baby blanket

Hi- I’m trying to get a baby blanket started in a ripple stitch pattern with a zig zag edge. The pattern I have says to cast on a multiple of 13 sts plus 2. I’m very confused by this - I have been trying to make a swatch, but one side edge is not straight, but angled in.
To make a swatch, I casted on 28 stitches (26+2).
Row 1 says: *K2, inc, K4, sl 1, K2tog, psso, K4, inc: rep from * to end. I don’t have a problem understanding these abbreviations, but
I think I’m doing something wrong on this row or I’m not casting on the correct number of stitches for this pattern to work out right. Can anyone help me?

I have casted on 52 +2 sitches to test your pattern. You did not indidcate what kind of increase you used but I tried it using a yarn over and it works out. You just repeat the Knit 2, yarnover, k4, sl 1, psso,K4,yarnover end with knit 2.That means the last 2 stitches are the +2 added to the multiple of 26 . I don’t know if every knit row is the pattern but I tried it that way and it works out. I just purled the backside straight, no increases or pattern. Just trust your instincts. The yarn over is the required increas, not make 1. The cast on edge will be kind of zig zaged due to the pattern, that is normal. The upper bound off edge will have the corresponding zag where the bottom zigs. Hope this helps.

If you use a kfb for the inc, it won’t work out. That uses 2 of the 13 sts in the repeat, so you need to do a YO or m1 where you pick up the yarn between sts, or a backward loop m1. The sl1, k2tog, psso decs 2 so your sts stay the same.