York e z curl bar questions?

hi 2day i went to argos and bought a york e z curl barbell weights set. Im 15 and i have another set of weights. The weights i have are one handed ones so you only use one hand to lift them. This has led to some problems with my ez bar. As you lift with two hands when using ez bars this feels very weird to me and the part which im holding with my right hand seems to dip whereas on the left hand side it doesnt dip at all.also the ez bar and the weights arent that heavy(18kg which is nothing) however, despite the fact tht ive been lifting weights for over a year they feel much heavier than they should considering the fact that i can pretty muchlift the sameamount of weight in one hand.Are all these problems im having due to the fact that i am not used to lifting with two hands an has anyone else found that at first e bars feel weid.