Stop comparing yourself to others. You don't know what they had for breakfast or how many workouts a week they do, etc. It should be all about you and what you can achieve.
Try to improve yourself. Always try to do more than the last time; think progressively, such as, "Today I am going to pick up the five pound dumbbell instead of the two pound dumbbell."
At the gym (or at home), stay on your own mat, mentally and physically. Remember we all have special strengths and abilities. Keep on keeping on, your fitness will blossom.
Just be you!