What is the pattern name and a link?
If there is a pattern stitch the best way to increase is to do a multiple of what're that is. Take ribbing for example - a k2p2 rib is a multiple of 4. You need 4 stitches to complete one repeat. So you need to figure out how many stitches complete the repeat and increase accordingly.
That is not always possible of course if the pattern varies. you may need to just put a wider border. Since I don't know what pattern it is I can't say for sure. It may be possible to just double it.