Give it time, and keep practicing. Practice is the key.
Sometimes, it takes a little time for someone to catch up but eventually everyone does. Do not worry about the less marks you are getting right now, just aim for improving yourself compared to the previous tests. Don't be distracted by the marks everyone else is getting. Not everyone is the same. Your competition is with yourself. Just make yourself better than what you were yesterday.
It's just the beginning. You don't even know what is ahead; you might end up being really good later.
But for now, don't measure your potential with some tests marks. Work hard and keep practicing.