It's all about the flexibility of your mind! Remove the urge to compare yourself to others, we are each built differently and have lived lives - giving us all different bodies. There are modifications for every pose, you can ask the teacher after class if a certain shape doesn't make sense in your body.
Once you are in the room you will see cork blocks and straps - these are helpful tools that can enable us to open the body in more ways. Take 2 blocks and a strap to your mat, experiment with how they can work for you. Ask the instructor for options!
Ultimately this is a no judgement space, yoga brings peace into the body and you can begin right as you are / where you are.