Yes, you need ailerons. How much depends on your plane and throws.

Is it the tail that is not coming down far enough to make it flat or are the wings not level.

If the tail isn't coming down flat try adding some more elevator throw. I use 50 degrees on my Edge and it is perfectly flat at a little less than 1/4 throttle. You will probably need a lot more throttle on yours though b/c your thrust to weight ratio is probably not going to be anywhere near what mine is on your .40 sized airplane.

I also usually always keep my aileron almost all the way in the corner. Just have to watch the plane and see if it needs a little more or less depending on how level the wings are.