I feel like I have something similar - I find it very hard to socialise, find it hard making any small talk with 1 person let alone if I am in a crowded place.
Don't be embarrassed that you are that way - we are all different and we all have different skills and weaknesses.
Try not to put yourself into situations where this would be a big issue, but as someone else said, set yourself manageable challenges - like speaking to someone on phone, going to store etc. Over time you will come to manage your anxiety - and you don't have to try and force yourself to become a small chat expert or anything, rather you will learn to accept who you are and to feel confident in public even if you still don't talk or engage with people that much- not everyone has to be loud and outgoing to get on in life.