Should i keep practicing this piece or just give up and say its too hard?
the Mephisto waltz is MUCH more difficult just so you know. Don't go rushing into it because you can play La Campanella. Yes, you definitely should continue playing this piece, as it will more likely than not be required at a competition at some point or another. it is standard repertoire.
No way. Mephisto Waltz is harder than La Campanella to master also. Here's proof:https://www.piano-e-competition.com/La Campanella and Mehpisto Waltz get played many many times, and Mephisto Waltz is completely bombed almost every time, and these are professional pianists.
In that, I agree with xvimbi, it's all about arm coordination, not fingers. I hope to God you're not trying to play this piece with just fingers!