You need to go back to where you had 21 sts, that's way too many. The pattern itself
calls for 25 sts, and the repeat is over 4 sts. The border is actually 9 sts, not 4 - 5 at the beg of the row and 4 at the end that's the sl 1, p1 k1 twice. It's probably a good idea to keep the extra sts in because that helps keep the scarf from curling.
Let's just go to R 2 which is the lace pattern row -
Sl 1, (p1, k1) twice, *yo, sl 2 knitwise, k1, p2sso, yo, k1; rep from *, end (p1, k1) twice
On this row, slip the first st (or knit it) p k p k, then * YO slip 2 sts as if to k2tog, k1 st and pass the 2 sl sts over it, yo, k1. Repeat everything from the * You have 2 YOs, but the dec is a double one so your sts should be the same.
Watch that at the beginning of your rows that you have the yarn held out a little at the side. If it goes to the back over the top of the needle that makes an extra stitch.
Row 4 is similar, but it's offset from row 2, starting at the middle of the lace pattern.
Sl 1, p1, k1, p1, ssk, yo, k1, *yo, sl 2 knitwise, k1, p2sso, yo, k1; rep from *, end yo, k2tog, (p1, k1) twice.