Thank you Carol and Nicole!
I think I have it figured out now. I did some fiddling with my tension and ran *very*slowly over any bulky seams and it seems like that did the trick.
I did break a needle though and ended up having to re-thread the entire machine (not easy when the bulb is broken and I can’t remove it for the life of me).
In the end (after having to go over the waistline seam twice because the fabric had gotten away from me I realised I had sewn the waistband on wrong (I twisted it 90 degrees on the Nature Walk Pants so that the side seams of the waistband ended up against front and back seam of the crotch.
Clearly not my night.
I was going to cut out a Hopscotch for Sofia but I think I’m gonna cut my losses and get a dose of Doctor Who instead.
Thanks again ladies!