snafu

I finally hit the wall with the tartan jacket. It's been problem free up
'til now. It's the increase in the collar. How does one increase three
stitches in a two-stitch, two-row pattern (similar to the seed stitch
pattern) so that the stitch order does not get messed up? This is an
example of the stitch pattern in number format. The numbers represents a
different type of stitch.

1212121212
2121212121

How can you insert three stitches in the middle of the pattern and not mess
up the continuity? No, you can't add at the beginning or end of the rows.
I think I will have to do an even number increase more frequently so that I
end up with the same number of stitches and rows as the instructions indicate. I've got the Excel cranked up.