Here some ideas:
#1 Try to create a referral program where someone signup for the waitlist will rank higher if they invite someone else. Or try to give something in exchange. x% discount in the first order.
#2 Spread in all social media channels and explain about how can be useful for users. Don't stop making videos everywhere every day.
#3 Add the landing page in all the beta directories possibles.
#4 Reach network. Send messages and emails to everyone to join the waitlist.