Greetings and welcome to B&B!
For most of us our neck whiskers grow asymmetrically, so taking the time to properly map the direction of your beard growth is essential. Also trying for BBS on your neck is probably not a good idea when you are first starting out, and really not necessary anyway. A lot of us, yours truly included, are happy to settle for a clean comfortable shave on the neck and don’t worry about a little stubble here and there. Technique is important here, of course and it really boils down to a lot of practice and trial and error until you get it right, and ‘right' means whatever is right for you. Here is an excellent thread on neck shaving issues which I strongly recommend.
Glad you joined us and enjoy the shaves!
Neck irritation