Sim mode correct?
Ok... i had this problem today on capture the airfield (i dont use the spit for that particular game mode and if i do..its to fight, not capture) but i had to capture today and each time i nosed over. To solve it (worked for me everytime)......
I came in on approach, and on touch down i kept my rear wheel OFF the ground, so basically i was still on two wheels, and then i gently let my plane bring its own rear wheel down. It takes time and patience, its "sim" mode for a reason
Just relax, and try it again soon.