Exposed to someone with Mono? HELP!!!!!!!!?

We were told tonight at church that a kid in my youth group has been diagnosed with mono. We were in close proximety to him on sunday night (I sat one chair away from him, we all touched the same nerf ball, ate out of the same Doritos bag at snack, etc.) HE NEVER MENTIONED HE WAS SICK! From what I'm reading, Mono is VERY serious and VERY contagious-- and once you have it you remain a carrier for life. So my question is (particularly to doctors, EMT's, nurses, etc.) what are the modes of transmission (I never kissed this kid or shared a eating utensil, but did sit one chair away--what if he coughed or spit while he talked?) and how long is the incubation period? HELP! I'm so scared--I dont' wanna catch this terrible disease! Also, can you have a blood test a couple months after exposure to test to see if you have mono? If you've had mono or are an expert, please comment!