Southpaw attempting to shave the neck

Keep at it! Things get better

Time n patience is needed to master a straight...took me 2 months to completely shave my face WITH my DE when I started over 2 yrs ago

Lefties and righties share the same problem, i.e., shaving the other side of your face. Not only am I left handed, I may be the most left handed person alive, but I was ultimately able to learn to use my right hand.

Since you specifically mentioned your neck, using only your left hand, try shaving the left side of your neck N-S and the right side of your neck S-N. When you flip the razor upside down, it's much easier to shave the opposite side of your face upwards. When you use two hands, you can also overlap a bit (shave downward past the centerline of your face, hitting some of the right side, at least past the right edge of your lips). That leaves less to shave downwards with your right hand. Similarly, shave the entire right side of you neck upwards, covering as much real estate as you comfortably can on the left side of your neck.

In other words:
Shave the left side of your face N-S with your left hand, covering as much of your right side as you can.
Shave the remainder of your right side N-S with your right hand.
Shave the right side of your neck S-N with your left hand, covering as much of your left side as you can.
Finish shaving the left side of your neck S-N with your right hand.

This technique will allow you to start on the easy parts (eg: it's easier to shave N-S with your right hand near your ear than your nose) and then gradually spread out as you gain confidence. I find I can now shave just as well with either hand, particularly in the S-N direction, something I would have never thought possible.

Using that "odd" hand while straight shaving is going to take some time to get the technique down. I know it took me quite a bit of time, but all at once things will just seem to fall into place. Be sure to do only the easy parts of your face at first, and only go with a WTG stroke. As you get better you'll be able to move on to other parts of your face. Also be sure to use no pressure at all. That may be the hardest thing to get down.

Ditto on Ouch.

I am hardcore right-side dominant. Writing, music, shooting, and shaving.
Shaving with carts or DE, I'm 100% right hand.
In many of my activities, my left hand is just a lump.

Straight shaving, I am completely ambidextrous. I tried right-only and I wasn't working.

Right hand, right side N-S to just beyond center.
Left hand, left side N-S to just beyond center.
Right hand, left side S-N to just beyond center.
Left hand, right side S-N to just beyond center.

Buffing touchups as needed.