https://knitpatons.com/en/free-patterns/julie
Keep in mind that the decreases are at the armhole edges for this part of the front. For the left front (left side as you would wear the jacket) the armhole edge is the beginning of a right side (RS) row. For the right front the decreases are at the end of the RS row.
You can place the decreases one or two sts in from the armhole edge. That’ll give you a nice edge for seaming.
So for the front on the smallest size, for example, the decreases are on rows 1,2 and 3, then rows 5,7,9 and 11; finally, rows 15 and 19. These decreases on left and right fronts are going to give you the same shape as the back armhole on each side.