Should I learn to use two hands?

[EugeneKim]

I played 1200 games so far, and I usually play 'difficult'.
I always used only one hand, but tried to change to two hands a few times.
However, when I try to play harder songs, it is very hard to play with one hand.
Is it OK to keep playing one hand, or should I change so it might be hard at first but I can be better?
When I tired using two hands, it really confused me, so I had to give up.
I also want to know if there are people that can play very hard songs using one hand.