It looks quite clear to me in the photo that your right shoulder is higher than your left, not lower.  I think that can occur through always keeping your shoulder positioned to stop a bag sliding off.  The neck is ok so you need to change the angle of the shoulder slope and lift the armhole, then look again.
I have the same issue - it is surprising how different your shape can be each side.

I did try snipping off a teensy bit of corner @ iminei, then a teensy bit more, then a .......... But it was just the same leading me to think i had got it wrong at the folding stage.

I know how to get nice corners on narrow quilt binding but as soon as I try to do wider binding I can't get the corners to be nice and square.  They just end up rounded with the corner of the wadding squished down.
Ive just been trying to do a 5/8 inch binding using a 3" strip folded in half but I've given up and trimmed off the excess wadding and reverted to a narrow border because I just can't get decent corners.

That's very useful.  It's something I've been intending to do forever to house my interchangeable needles.  They're in the plastic, zip up case they came in but the needles are attached to a piece of card with elastic and i have bought a couple of extra sizes which are separate.
Having seen yours I will resolve to get on with it.  There, I've said it now 

I never trust the grid on the cutting board, I don't think it would be accurate enough.

I think I would fold the fabric into 4 lengthways ( ie selvedges together then in half again) then measure down and mark 6½" each side to cut wof strips.then leave each strip folded in half and do the same to cut pairs of squares.  A bit laborious but with a quilting ruler you can at least be sure of getting 'square' squares.

or
I would buy a 12" square ruler 

Can you work wearing earplugs @Bill ?

@Ouryve are you allergic to the metal button?  I have a metal allergy but I always have a t shirt tucked into jeans.  I even have issues with the hooks on bras even though there isn't direct skin contact.

I think a lot depends on the density / weave of the fabric.
I am currently sewing a water repellent cotton, it is not a heavy fabric at all but a very tight weave and  ' coated' to make it water repellent.  I cannot get a pin through 2 layers of the fabric - it's not easy to put a pin in one layer.  My Pfaff is happy to plod through multiple layers of much thicker denim or canvas ( with care) but I don't think it would cope with the same number of layers of this fabric.  It did go over 2 flat felled seams but I used the handwheel to get the microtex needle through.