This is normal on a nitro car.  You'll usually always spill a little but whe you are filling it, and that fuel seeps all over the placte.  There is a lot of oil in nitro fuel and it won't evaporate like the fuel itself does.  You will also get a lot of oil coming from the exhaust which ends up all over the car. Nitros are dirty, but a whole lot cooler than toy store electrics!