You said you had one before but that was size m which was too loose and now s is too tight? Or did you have one in the same size?
You might want to consider that your head and the lid aren’t a very compatible shape to fit both ok in terms of size and shape.
I know that my head fitted well in a Shoei xr1100 but not in one of their other models (can’t remember name). It would kill me.
I was lucky in that the first time.i.got one the guy in the hein gericke shop insisted I kept it on in shop.for about half an hour. I must have looked like a lunatic walking around with it on.
As others said, try different pads and patience if it doesn’t fit. I wouldn’t try to ‘stretch’ it at all with ball or other method. You don’t want to damage the integrity of lid by applying pressure from within! It’s for your head so if it doesn’t fit after new pads and patience, you may have to chalk it to experience, sell.it second hand for a.bit of cash, and go and try others properly in a store.