Feeling nervous when starting something new is very common and normal. It is completely okay to feel nervous. Regular activity can reduce anxiety in general (1). Exercising with friends and family that you trust is a helpful way to overcome these anxieties e.g. with family, with friends or after-school clubs. Look for different strategies to overcome this.
Tips you may wish to share
Look for activities that appeal to you and you think might be fun. This may be something that you have seen your friends do and perhaps you have previously been anxious to participate. You should feel comfortable with whatever you do.
Move/exercise with a friend or family – it can be more fun.
This can be group activities, or if you prefer can just be being active by yourself in your home to start with.
Are there people that you look up to who are physically active – maybe they can be an inspiration for you
Ref(1) Annesi JJ. Relationship between self-efficacy and changes in rated tension and depression for 9-to 12-yr.-old children enrolled in a 12-wk. after-school physical activity program. Perceptual and motor skills. 2004 Aug;99(1):191-4.