I've been thinking about your sleeve issue. I think I visualize what is happening now that you have given me more information. You said you are knitting in the round, but you also said this is a cardigan and you are knitting and purling so I assume you meant that you were working on a circular needle but not really knitting in the round.
I looked in a book I have that has a saddle shoulder sweater in it so I'm understanding better where you are at now.
Next directions say:
Set up Row: (partial) K15 do not turn.
R 1 (RS) Cont over sleeve sts ,sl 1, k16,ssk, turn
R 2 (WS) S1, p16 , p2tog turn
Rep rows 1 and 2 until all sts of right side have been worked ending on a ws row
You are going to be working back and forth across only the sleeve stitches decreasing them away to form the saddle.
I see your problem. Since you just finished a RS row and are at the center front of the right side of the sweater, or are you?
I understand most of this except I'm guessing I need to join new yarn here if I need it on the right side, because I ended on the right side and my yarn is on the other (left).
Are you saying that your yarn is on the left front of the sweater (as worn) at this point?
Yeah, either way it doesn't quite work out and they don't tell you what you are supposed to do in much detail, and it seems like it would. If you were at the sweater's right front edge, you would be turning for the next row which would be a purl row, so the next directions wouldn't work for that. OR if you are at the left front of the sweater now you can't just start working on the right front. It sure seems that they have not told all they should about what to do next.
If they want you to start a new yarn on the right front they should say so. If you are at the center left front you would need to begin on a purl row, ditto if you were at the right front and it doesn't say that either. Errata is a good idea. (or possibly you made a slight error somewhere that made you one row off?)
I would read through the rest of the directions carefully to see if I get any clues. Then you will just have to decide on a way to proceed that makes sense and will work on both sides the best with the further directions you have.
Your options seem to be to turn and work the first row as a purl row instead of a knit row (and if you are on the left you would be doing the left shoulder first). Since there is shaping on either the RS or WS I think this would work....unless there is something that you can think of with the further directions that would be really fouled up that way. LOL You may be able to make a slight adjustment in the directions further on to get that to work out.
Or you can attach a yarn to the right front so that you can work that first row as written.
I think I favor the first option, but you have it all in hand and will have to decide what you think will work out best. Talking about it always helps you think it through, even though the call will have to be yours. Good luck. Let us know how it turns out and what you decided to do.