I feel for all the posts like this, because I was a worried mommy about my little Mazie, too! She was less than three lbs (at 11 months) when she was spayed, and the vet wasn't at all concerned, but I was!
But girl, she came home, no antibiotics, no painkillers, no cone, never thought twice about her stitches, and never acted the tiniest bit sore....just straight back to being her little monkey-self, and we couldn't stop her!
Good luck! And WEIRD about the heat!