@LaChanticleer @CloseYourEyesAndSee and others, you are all right.
I am of a short and stocky build, and I need to come to terms with that. Honestly, 99.9% of the time I am content with my body shape, but this bloomin' dress has me second guessing myself. I'm slightly regretting the dress neckline... It looks great from the front, not so much from the back
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@RJnomore1 @Nevilleslongbottom thanks for the kind thoughts that I've lost weight
- haven't lost on the scales, but my body is a bit smaller, which is why I thought I'd lost fat and gained muscle.
With my neck, you're all right, I think scrutinizing it in the mirror / TV as I work out has made me look at it more closely and notice things which I haven't before. I have a very defined 'slope' from neck down to shoulderblades, and then a definite 'dip' where my bra straps lie. It's not a smooth nor level shoulderline. But then that's my shape, and I need to make peace with that.
@reallyworriedjobhunter, thanks, I could consider a shrug - I'll keep that as a back up plan. But I'm going to try to be happy in the dress first, just the way I am. 
@Deux, this is useful - for exercises like rows and RDLs, I should be pulling my shoulder blades together, and so not feeling it in my traps, is that right? Maybe also for shoulder presses?
I do wonder if my posture isn't quite right for some exercises and this is exaggerating it. I will go back to the start and recheck how I do each exercise.
@Thissucksmonkeynuts@Ahoyashipg, I'd love a pirates instructor
, wonder if I can find one of those down my local docks...
Everyone, thanks for the pep talk! This was just what I needed. You're amazing.