Hi Rob. I said there would be better advice from here
One thing I've noticed on your buck is that your backbone looks a little flat at the top, making the transition between the stations difficult.
I always try to remember when I'm raising a shape that if a section is touching the buck, it needs more shape at that point, or the surrounding area needs shrinking to bring it down.
As I think that this is a practice piece for you, Is it possible to doctor the buck - i.e. bring the adjacent stations down a little to give more shape to the top? Probably doesn't need much.
In terms of shrinking the overstretched edges, I'd be looking at using a tucking fork and a stump. The Lancaster is a pain to use on an edge once the edge has some shape.
Personally if it were my practice piece (and bearing in mind that I'm a newbie at this too) I'd be trying to gently add more shape in the middle and then wheel out the lumps.
Don't be afraid to wreck the piece and start over - you will close in on the shape many times faster having learnt from mistakes on the prototype.