Well saying you have no weakness's is a weakness in it's self, as you fail to see any weakness in yourself may lead people to believe you're too confident....there's your weakness.
everyone can improve on something in flying, there is no such thing as the perfect pilot. point out a weakness or a past weakness which you are or have already ironed out due to something you have done to correct it or are in the proccess of correcting and they'll see that you are driven to self improve. they don't want people who are content with being just ok or good enough, they want people who want to always improve, learn new things, approaches and just simply maintain high standards for themselves.
hope this helps....