Is it possible to derive a superlative form of right (meaning the opposite of left) - the rightest?
Rightmost would fit here.
Incidentally, leftmost for left.
Not quite one word, but you could use 'farthest to the right' or 'farthest to the left' as the case may be.
When you use 'Right' as in correct, the superlative form becomes 'Most right'. English, right?!