ANSWER:

You must not pay attention to such doubts if they come after you have performed the act of worship (wudu in your case) and especially if this (doubts) is a reoccurring thing for you.

I performed wudu then when I had started praying . I felt my arms werent wet.now I had doubt whether i washed my arms and wiped my head. I had already started to pray, what should I do?