@Scarednconfused
I am so sorry you are suffering, mental health issues are hard to deal with,, and bi-polar is a mean one!
But surely you must have known about how you are/how you would be, when you booked everything, and invited 150 people.
This is going to cause a lot of inconvenience, and stress, and financial loss for you/your family (your parents if they paid some or all towards it.)
I get a bit stressy and angsty in big crowds/big group situations, and hate being the centre of attention, and so me and DH had a small wedding with only 30 people, and a meal at the pub after. (No big reception or night do.)
Why on earth did you arrange this massive event with 150 people, if you know you struggle?
I think you need to try and push through it. It's only one day, and it really is too late to back out now. You will have a LOT more stress and angst trying to cancel, (and having to deal with the fallout afterwards,) than just putting on a brave face for one day.
Sorry if that's not what you want to hear. But you did ask, and that is my honest opinion.