OP here with a small update...
Last night DH and I ran into one of the moms of DD's classmates and asked if her daughter would be able to make it on Sunday. She told us she didn't know yet and would let us know later. Shortly before DD's bedtime I got a phone call from a parent of a classmate and they are planning to be there. So we will go ahead with the party as planned and DD is super excited that a friend RSVP ed and is coming on Sunday.
I still don't know about a few of the family and friends that were invited, but this is par for the course and I don't feel guilty about changing things on them as they don't seem to worry about RSVPing until the day of sometimes.
It will be interesting to see how many other classmates call between now and Sunday or just show up Sunday. My plan is to have stuff ready for goodie bags, but not open anything extra if I don't need to, so I can return items if unused. DD is super excited to go pick out her cake today and to prep for the party, but I did tell her that from here on out it will be sleepovers or 1 or 2 friends at a time.
eta: Thanks to everyone for your help and suggestions. Hope you all have a great weekend.