My pattern calls for Merino Aran 18sts and 26rows =4" the back has 79sts. the finished sized is 34". My question is, if I changed the yarn to 20sts=4" and cast on the same stitches will my pattern turn out ok with 31.6" finished or will the pattern be too far off. My sweater that I wear is 32" finished when I lay it flat on my bed But when I measure myself I am 34" I can't figure it out because the sweater is not tight at all. I just don't want a big baggy sweater. I did not go to weight watchers to hide my self.