Hello dear! Can you tell me which version of the pattern you have? That way I can make sure I am looking at the same one. There was actually a couple of updates, but I do not recall either having any changes to the neck or the straps.
The first strap, should have been connected in the front, and then whipstitch to the back. I am not sure what size you are doing, I am going to assume the 2T since you mentioned working 24 sts along the strap (and that coincides with the 2T), but this first part will be the same for all sizes: When you start neckline, you want to connect to top back corner. If you refer to page 3, there is a diagram. The second diagram will show with an arrow where you start this neckline.
However, I am puzzled at the strap issue. I just checked the math, and the 30 sts in for the first strap for size 2T should put you in the front of the Band (thus making you whipstitch the last row in the back). When you worked the strap, was the first row with RS facing? But even then that would still put you at the front, you would just have the opposite side facing. Can you tell me how many free loops you have between the edge of either strap to the top back corner?