Penalties for Subsequent charge while on probation in VA?

Ok well basically I got pulled over with beer in my car and I took the rap for the underage possession. So I went to court and I have a deferred sentence which basically means I have to be on "probation" until i complete 50 hours off Comm. Service. I also only have to meet with the probation officer once a month. So last night I needed a ride home from a party and these seniors from my old high school give me a ride(I am 20 ). The kid runs a red light with police right behind us and unfortunately I had under a G of weed. So basically I just want to know what can happen and how can I help myself. Obviously quit smoking, which i have made the decision to do, but is there something else I can do like do more hours of community service? or something take substance abuse cles? What makes me very scared about this situation is the fact that I had a Poss. of pot charge but it was dismissed. So would this be like a first offense.