An easy way to join seams for raglans is to seam the back to each sleeve at the long line of the raglan decreases. Then seam the fronts to the sleeves again along the line of decreases. When you do this, the sleeve top becomes part of the circle around the neck. Then it becomes easier to see where you will pick up sts along the sleeve top for the collar. See if looking at some of the pictures
of projects on Ravelry helps.
The raglan seam isn't like the usual set-in or drop sleeve in that these sleeves usually don't form part of the collar.
Very pretty cardigan!