When doing wudhu, after washing my face I forgot which side of the hand to wash first. I thought it was the left side, and began pouring water on my left hand. After a few seconds I realized the right arm should be first. So I then followed the correct procedure and completed my wudhu. Is my wudhu invalid because I mistakenly began washing my left hand first?

In such a case you should start your wudhu again by washing the face