有错.
U(主)will never think(谓) it(宾) a waste of time.
句子主谓宾明确.后面不能跟名词a waste of time.
如果你想表达的意思是"你从来都不认为这是在浪费时间"的话,可以将句子改成U will never think it's a waste of time.将后面的名词改成宾语从句,就可以了.