Problem with joining shoulders/seam

Above is the pattern I’m using for the sweater jacket. I am at the finishing stage and I joined the shoulders/edge of neck. I did the sewing for the garter stitch, at the edges. My seam is very noticible, not like is should be. I don’t know what I did wrong. Could I use the stockenknit stitch to close my seam? As you will notice the top of the back and tops of two fronts are not straight, they do a gradual tapering which I think has let to the messy look of the seam.

If I were doing this I’d work short rows for the shoulders and, therefore, have all live sts. Then do 3-ndl BO on them for a neat and sturdy seam. The st patt perhaps gave you problems trying to obtain a clean seam. If you want to undo your seaming and consider doing the short rows, one or more of us can walk you thru the process. (There’s vid for short rows, aka wrap and turn.) 3-ndl BO works great on sloped shoulders (after the short rows).

BTW, ‘stockinette’ is a knitting stitch…not a seaming stitch. If part of the shoulder slope is st st, part is garter, that could be complicating getting the finished look you want. (You probably also have ‘steps’ created by the BOs. Those are eliminated if you do the short rows.)

ETA: you can also look here:

at the chapter on ‘Horizontal Seams.’ There’s info on shoulder seaming (with steps) but, as I recall, the examples have st st.