"These anxieties and worries are rarely a reality."
Whilst you ask yourself, Is everyone watching me? Will I be able to keep up? The truth is, the majority of others around you share the same worries; it's normal. However, realistically, when you do attend an exercise class, everyone focuses on themselves rather than others in the class, so these anxieties and worries are rarely a reality.
"Find a friend to attend the class with you."
The more you shy away and avoid attending these classes, the more anxious you will feel to ever start going and a vicious cycle of avoidance anxiety will begin. Once you take the initial first plunge, it will get easier from there. Perhaps if you feel super nervous, why not try and find a friend to attend the class with you, or position yourself in the room somewhere that you feel most comfortable, whether that is right in the back corner or in the centre of the front row. Exercise class anxiety is a real thing but it's not something that you can't beat.