You just knit the set-up row for the cable pattern. You're right that your stitches will have to line up properly to follow the chart.
One thing you can do is look at your stitches as you knit them as you read the directions for the first row, and you should be able to tell where your mistake occurred. Mark the stitch with a little piece of yarn and you can work those together on the next row.
Another is to tink back to where the error occurred and continue from there.
I don't think it's wise to just p2tog at the end, because you don't know where the extra stitches are.