What do I do about extra stitches caused by vertical joins when joining horizontally?
Not sure what you mean. Can you post a picture?
A three needle bind off is used to join blocks. I have done all the vertical joins. Now I. Will use the same three needle bind off to join the horizontal rows, but the stitches don’t match because there are more vertical joins on the top row than the second and more on the second than the first. It’s the nine patch blanket in the Log Cabin Field Guide.
Skip a stitch when needed in the middle of the block, not on the ends, so it won’t show.
My instinct says to skip over the vertical joins and then use the tail that you will be weaving in from the yarn that you used to do them to snug up the teeny little gap you might have there.