Sorry but you sound so much like a stroppy teenager and not like a grown women.
Your thinking sounds very unempathetic and rigid.
Nope, it wasn't ''a spat " and you hurt your SM very much.
Nope, your Dad's house isn't always just open to you.
The fact that SM has "always been good to you" is passed over as if it means nothing but you don't acknowledge at all that your father was ultimately responsible for your relationship with him and his new family.
Just the idea that you are sitting there telling your SM that she won't really be a grandparent and reeling off who will be called what when your child to be hopefully is born, sounds so immature and lacking in experience of what goes on in the real world. Its is a fact that children all over call all sorts of people all sorts of names, in all sorts of different types of "grandparent" relationships, step, blood, foster, adopted etc etc and love them dearly and BENEFIT from having them in their lives. You don't get this at all.
Personally I think you said it because it gave you the one up over your SM. Classic Teen.
Expecting to be taken on holiday to Disney Land as a grown up just shows who you are still locked into that way of thinking.
I suspect this 'shot' was the straw that broke the camel's back for this SM who "has always been good to you." With respect to her family you sound toxic.
Grow up. Take responsibility for your feelings and get counselling to help. Choose a happy relationship with your Dad and SM and siblings whom you love. This is also for the sake of your future children.
Good Luck with the IVF.