You are three hours behind us. I would say 'us' instead of 'me', it sounds more natural in English to refer to everyone in the time zone rather than just yourself.

se dice: En relación a mí, tienes tres horas de retraso.

En relación a mí, tienes tres horas de retraso

"You are three hours behind me." Just to contrast with Paul's answer (since he's from the UK), the above expression using "me" would be just fine in Canada (and assuming the listener knows you're already talking about time zones, for context).