I believe that electric plane is designed to be hand launched so that would explain why it turns if you try to taxi it. As far as why it turns when you hand launch, there could be a few reasons. Hand launching is best done by a second person until you get used to it. It needs to be launched straight, level, and slightly upward. You have to be ready to apply slight up elevator and roll correction if needed, (that would be rudder if it's a 3-channel)
Wind could also be a factor with this type of plane, try it when the wind is calm.