Any gap at all makes a difference to the control surface response. I would try to get rid of the gap.

If you covered the model in film use a strip of film along the top surface. For example, on an aileron, push it down to full deflection, stick a strip of film down to the wing then across the gap and onto the aileron. Don't try to shrink it. When the aileron comes back up to neutral position the film should sit down into the gap sealing it off.

With the gap sealed there are a couple of advantages: the effect of the control surface is heightened, ie more powerful; and it helps stop control surface flutter at speed.