Hi Pat - you know what I'm going to say.
I will change my approach, though.
I changed the playback speed in Youtube to .25 - this really helps to see what happens when.
First, yes, you should push your ball in the direction of your target in order to begin a good swing plane. I'm also in favor of walking toward your target.
Second, your swing plane changed at the top of your backswing. You can see the left-to-right movement at :21-:22 and from that point, the ball falls "out" and not straight vertical. This is the result of muscling - your ball should be at the top of your backswing at the second-to-last step so your final step is all delivery/slide. In your case, your ball is at the top of your backswing at the start of your last step
, in other words, early, so you have to pull it back down.
Pulling it back down is nearly impossible without some pulling to the side - because our muscles don't work that way! The muscles that pull our arm down, also pull it inward (leftward). That's the reason (well, one primary reason) why we try to have a completely unmuscled, pendulum swing.
This is a huge indicator to me - when I start being unable to get the ball right (out) it's a sign that my ball is late, my feet early, and I'm muscling the ball to get it to catch up. It's also harder on my left (slide) knee.
For you, on your three step approach, you need to start your feet later - you're starting your third-to-last step WITH your push-out. This means your feet are now well in front of your ball. Starting your feet later (with the actual drop of the ball, not with the pushout) will allow your ball to get solidly in your drop, and then backswing along with your second-to-last step and let that step be more of a stutter/"co ck and lock" step gathering up your power, and then when your ball is ready, you can step and slide into your last step and the ball will fall, on its own (it's gonna fall. . . you can't do nuttin about it! LOL) through delivery - and you won't change the swing plane (well, ideally!) You'll also be able to be more vertical, which helps with balance and your lower back and knees (and BOY do I need that! Whew)
You're not doing it badly. . . when I'm tired and unfocused, the direction of the ball can go 5 boards left at the arrows - that's bad. Yours is pretty much going straight. . . which still, you're wanting it to go out a bit.
If you want to stay three-step, here are my suggestions:
1. just do a slide-step approach drill. This will give you the "feel" of what the ball wants to do. Notice that none of these even care where the ball goes (well, forward, obviously! LOL) but they allow you to feel your body staying upright, your slide and balance foot being nicely set.https://www.youtube.com/watch?v=1DrO7EC4Jy4 https://www.youtube.com/watch?v=QZ23LKBLemwhttps://www.youtube.com/watch?v=51Irk6bGFpY
2. Then move to integrate that with your three-step approach. You can look for "three step drills" - same thing for you. You're using a "drill" for your whole approach. Here's one and he talks about the balance and "feel" all the way throughout. https://www.youtube.com/watch?v=pDZra4G0jFg
3. Now (can't help it. . . heh heh) - I would recommend adding that fourth step to the beginning of your swing - it really is there for a purpose. If you don't want to, I understand. I'm completely stubborn too. However, it gives you something to do with your ball in preparation for the last three steps. Right now you're combining that with your third-to-last step which causes your feet to be ahead of your ball and your arm to muscle the ball.
Hope this gives you a couple of tools and helps a bit.