5 year old sons birthday party

Sooo.. this Saturday is my son’s birthday party. We sent invitations to school at the beginning of this month and his teacher said she put them in all the kids folders (19 other kids). We also gave them out to his tee ball team (9 other kids). Not one has RSVP’d from either. My son has been telling us how he’s excited for his friends to come to his party. We have a trampoline, a playset, and my mom runs an inflatable business and she’s bringing a bounce house as well. The only people in my family with kids is my cousin and luckily she’s only a year older so they play well together. I’m concerned my son is going to be upset that no one came and it breaks my heart. Have any other parents had this before? How do you navigate the emotions and explain to them why no one came? Any tips or advice is helpful!