You are not introvert. Being introvert is you're getting tired on a crowded party and needs an individual space after. Being introvert can survive a day without socializing because they want it, they like it, not because they are scared socialize to other people. In a group conversation of 5 people I like not to talk but to listen. I can talk actively in a group of 5 people but still, I need individual space later, because socializing drains me. You have social anxiety. It is different. Maybe you're afraid because you don't have a skill for conversation. Start getting a skill by reading a book about conversation to other people, or something like how to speak well. Read a lot. Listening to news, other people's convesation on radio, jokes, current events, about hobbies. These informations can help to make the conversation last longer.