Mitten decrease problem

I’m knitting mittens using a YouTube tutorial that starts with 36 stitches divided evenly between two circular needles (18 on each). The thumb gusset increases are made only on one side — starting with 2 stitches before a marker, and increasing the number of stitches before the marker each round, but always subtracting those 2 base stitches. Eventually, I have 12 stitches before the marker, which I set aside for the thumb.

After that, I continue the mitten hand and go into the decrease section. At this point, I have 20 stitches on one needle and 18 on the other, because the gusset was only on one side and no stitch redistribution was shown in the video.

The decrease pattern in the tutorial is:
k1, ssk, knit to last 3, k2tog, k1 — on both needles, repeated until 5 stitches remain per needle, then grafted.

But since one needle has 18 stitches (an even number), it can’t land on 5 stitches evenly — and the video doesn’t show when or how the stitches were rebalanced. I’ve already done about two rounds of decreases, but I’m willing to frog just the decrease section (not the gusset or anything before it).

What’s the best way to fix this? Should I redistribute the stitches (e.g. 19 and 19) before restarting the decreases? Or would you recommend a different decrease altogether — something clean and symmetrical that would work well for both the left and right mitten?