I did a lot of exploring early in the game and i got the quest "rattay tournament" from a smith in "Samopesh". So i travelled to rattay to compete in the tournament, but i don't have a chance to win a single round. I barely did any fighting so far, so my stats are very very low.

So i decided to do this quest later after getting some more experience in fighting. But i does not seem to be possible to do, because if i do not compete in the tournament on the same day in game, then the quest is going to fail.

Is there any way to continue playing without the quest failing?

***MINOR SPOILERS AHEAD***

the 'tourney/who do you like' quest only fails for the day. the tourney is held every few days, so you can enter as many or as few as you like. the structure of the tourney is to beat each opponent twice for 3 rounds, hence 6 rounds (as a minimum) one after the other, winning each one. the quest given to you by the blacksmith won't fail unless you are beaten in the tourney twice by black peter. he's usually faced in the third round of the first tourney
i might suggest training with capt. bernard, especially in defence and mastering the perfect block, and have basic training in all the weapons on offer. you might also want to keep an antidote handy. hope this helps!

The god awful combat system is what made you weak. It sucks so god damn much.