Slightly larger foam wheels would help.
Try an 11x5 prop for a little better acceleration or 10x6 if you are cutting grass
Make sure the plane is sitting LEVEL when parked and NOT nose low.
Recheck that UP elevator is "UP" elevator
Lower both ailerons a few degrees(more lift), easy if you have flaperons hooked up but probably not
More nitro will have a negligible effect
Check CG
Keep nose steering movements to a minimum as this creates drag
Taking out the baffle may help a tad as will good tuning

Good luck.

Oh yeah, hold the tail and run it up to full power before releasing it for takeoff roll. Not allowed at some fields though.