It may roll that way from torque. Try throwing it without power to see if it is the airframe doing it. Right trim in the ailerons or down/right thrust in the motor might also help. You may have to launch at lower power and then let it build speed before powering up. Without a rudder to keep it straight torque may have more effect than a conventional fuselage. Hard to figure out when all you have is a few seconds of flight time to watch it. Do you have a good zero on the ailerons? One might be a smidgen off of neutral.