i do not have enough gems to beat sarvern shepard
You do at no point during the game need to pay Gems to play or succeed at a level. If such an information is given to you please report it immediately to us as it is certainly wrong.
What I suspect you mean is that you don’t have the gems to buy equipment to beat Sarven Shepard. You will fight a total of 8 Ogre Scouts, 2 at a time. What is your equipment that you can not handle them? What did you spend your gems on instead of for example armor or a better sword?