Everyone cancelled on my birthday

I sent invites out a couple of months ago and of 30+ people, 16 said they’d come.
It’s themed from my fave film and I had accessories so nobody needed to make an effort with an outfit at all.
I spent a few hundred on decorations to transform my home, a custom cake, and food, and hours planning and prepping.
I’ve been so busy and stressed with work I was really looking forward to this.
One by one, everyone’s dropped out except my sister (who did try but needs somewhere to stay whilst visiting our parents).
Excuses are ‘I forgot and now I have another thing on’ I.e. never booked it off work (he starts in the evening and it’s a day bbq), someone forgot and bought festival tickets, someone forgot and agreed to go to someone else’s party.
Even my best friends of 15+ years.
The final 4 cancelled just today after I’d started putting decorations out saying they’d literally just forgot but are sorry.
I rang my dad asking if he wants to go to the beach with me instead and he said no.
Do I even bother? The cake is in the fridge. Probably half the decor is returnable.
My sister is coming, my husband has food poisoning, I could invite my mum over for numbers but I’m so defeated.
What do I do?
It feels like such a huge waste of energy after so much planning and money and time to then realise I’m not even enough of a priority to go in someone’s phone calendar.