Ahh, sounds like you're experiencing the dreaded torque roll. Are you hand launching the plane, or are you taking off from the ground?
If you're hand launching, try reducing power to about 50% throttle and giving it a toss to get air moving across the wings. That air movement is what generates lift. If you're just letting the prop do all of the work, the torque from the rotating motor is going to want to roll the plane - it's a major reason why helicopters have a tail rotor, to help counteract the twist of the motor.
If you're taking off from the ground, try rolling up on the throttle and letting the plane get air under its wings before you pull up, instead of going full throttle, hard to the stops. That'll help on the takeoff. My dad experienced the same issue, said his plane kept pulling to one direction, and by rolling smoothly up to full, rather than a "shove it to the stops" approach, helped him IMMENSELY.