We all need to make adjustments to patterns to get them to fit correctly; some need to make loads of changes and some of us are lucky enough to have only minor revisions. But I have yet to meet the person who makes no changes. (Well, OK, some don’t; but should. 😉 )
Be sure you draw or use a vertical alignment mark on your pattern to keep the correct grainline/pattern piece orientation. On the bodice shown above, I used the pattern’s grainline mark to keep the bodice back on grain when I shortened (petite’d) the pattern through the armscye. I drew a vertical line though the shoulder (anywhere is fine) so I could correctly align the top edge of the shoulder after adding extra length to the back for my forward should adjustment. This little extra step will really help keep you pattern properly aligned when you are cutting and slashing!