The decrease is going to disrupt the pattern at the edge and you won’t go back into the written pattern for a few rows, depending on the moss stitch you’re using. You can either follow the written pattern and take into account that you have one less stitch or you can begin to read your knitting.
Reading your knitting is a very useful technique to have. Basically, you look at the previous rows and determine how to work the current row so that you maintain pattern. So work your decrease and then look at the row below. If there’s a knit stitch, work a purl stitch on the current row and so forth.
Which pattern are you using? Can you give us a link to it or a pattern name?