When you take up a new activity or hobby, your efforts will often, sooner or later, be met with frustration. Understand that this is not uncommon and you are not exceptionally worse than the other students around you who seem to be excelling. What you must learn is the fundamental idea that YOU ARE NEVER TO COMPARE WITH ANYONE BUT WHO YOU WERE THE DAY BEFORE.
We are all unique and blessed with different skills and strengths, some of us having long legs, more coordination or different learning aptitudes. What can get lost in your journey is the fact that you began your Jiu Jitsu to achieve some form of self improvement. By learning to measure yourself only by whether or not you are improving, you will be able to better detect your progress in Jiu Jitsu which is sometimes all the encouragement you need to keep going.