There really isn't a "frontside" or "backside" to the actual slide - these more refer to the direction you spin out of the rail. That being said, there are lot of people who are very comfortable sliding with their right foot forward, but spin to the left, which sounds like you. It can be awkward learning that opposite direction spin at first, but you will eventually feel very comfortable with that as well. Stick with the sliding side you are most comfortable with at first - but I do suggest trying to slide both ways, this will be especially helpful with spins onto rails. Good luck!