No you really won't.  The majority of our worship is in silence so you will not be called upon to contribute so do not worry about that.  Sometimes an individual will make a contribution during the meeting but this is only if they feel they want to.  Even long-time members and attenders may not often, or have ever, said anything during a meeting for worship.  Coffee afterwards is a chance to have a chat with other friends but there is no obligation to stay for that if you don't want to.