Don't give up
It wasn'T extremly bad...just bad...Try to make the sounds equally loud, the voices were so quiet...then there was this LOUD blade sound that almost made me head explode with my headphones...so work on the volumes...just watch your own movie many times you'll know what doesn't sound right. Next time try to make full body characters, do the motions yourself with your body to see at what speed it should be, they all walked very slowly...try to think of more realistic plot and action sequences, ninja hides in the shadow, a guy with a huge sword fights longer.
Dont let the bad comment discourage you, you're 13 and you'Re doing this, most people who critic your movie never made anythign so just keep practicing and you'll get wicked good.
Peace