I only found one egg in my hair, do I still need to treat my lice?

Yes. Head lice eggs are laid at scalp level by sexually mature lice.You can have lice for ~10 days before they start laying& they are tiny & hard to see.You cannot assume that a casual mature louse laid one egg and then committed suicide. If it is there & really a nit, it means trouble. If you treated &just have a nit left over from prior infestation, just get rid of the nit & retreat if lice return.
Nits. Nits of head lice and pubic lice need the warmth and high humidity that is found near human skin to develop properly. If nits are removed from this warm, moist environment they quickly die. This is one reason why it is less important to treat the whole house, bedding, furniture and so forth because lice in general don't survive for long away from their host.Go ahead and treat for head lice.