Don't do public proposals, seriously. No one's going to be impressed, you are celebrating a momentous day in your life with a bunch of strangers like me who don't really care and you are ruining other people's night out with this type of gesture.

Find out what sort of proposal your girlfriend wants, I did mine with a few of our closest friends and the next couple outright said she will not do something similar, so my friend smartly did his proposal in private.

The only one I remember looked nice was one that the person booked the entire cinema (maybe you can ask for the time where there is least amount of people going, so they are much more willing to rent out to you cheaper?), he played a own movie he made with puppets and then he proposed, when the lights went up, she noticed it was filled with their family and friends. That is also after he knew she will accept and had no issue with it just not too public.

I'll try to find the clip if I can and if you want..

All the best to you. It is your special day, so enjoy it and ignore any of the negativity for now