122 in an 80 after passing

Hi folks, hopefully someone can help me out here or at least provide some advice/let me know what is to be expected, this is my first speeding ticket and I'm not too savvy on what the proceedings are here. I was driving Northbound on the 2 lane highway 140 between Port Colborne and Welland and had been driving behind someone going 60! I figured I'd wait for the truck in front of me to pick up speed, as we were only a few minutes from the beginning of the highway, however after waiting a few more minutes, the truck's driving speed was a bit inconsistent to say the least; accelerating and decelerating between 60-75. There was oncoming Southbound traffic, so I waited for my opportunity to pass the truck and when it came, there was a gap in the oncoming traffic of perhaps 500-600 meters before a long string of cars approaching. At this point the vehicle in front of me was hovering around 75, but I wasn't particularly comfortable driving behind it. So, I signaled and moved into the left lane and accelerated, but found myself needing to accelerate higher to actually be able to pass the truck, which I did, and moved back into my Northbound lane. A few seconds later, I passed the Southbound string of cars, and the second car in the lineup was an OPP officer. Immediately he threw his lights on, at which point I pulled over and waited for him to pull a U-turn and pull over behind me. He didn't really say very much; he told me I was driving awfully fast and I admitted my fault and said I had just finished passing the vehicle in front of me. He asked where I was going, I told him to my grandfathers and he took my license and registration and went to his car. When he returned to my car, he told me that he clocked me at 122 in an 80, and that it would be a $317.00 fine. He said that the OPP no longer performs any roadside reductions of fines, and that I would have to call in to the Crown Prosecutor to discuss a resolution (or that I could plead guilty and pay the ticket, or appear in court). I'm not really sure how to go about this from here. When I read the back of the ticket it says I'm supposed to meet in person with the prosecutor but I'm not sure what to tell them. I didn't realize that you're not actually allowed to surpass the speed limit to overtake a vehicle in front of you, but I'm not really sure how else to pass someone :? I suppose that my only option was to stay behind the truck, which I guess I should have done, but I've already gone ahead and done it now, so I can only move forward from here. I don't know whether or not the officer had the speed of the truck behind me, but I'd imagine that he didn't radar it because as soon as I passed the police car, he put his lights on and U-turned once he passed the truck and all of the vehicles that were behind us, but I can't really be sure. If he did record it, would this matter at all? Because if the speed of the truck were anything over about 75 it would be evidence that it did in fact, speed up as I was trying to pass it (which I suspected at the time but was more concerned with getting around and back into the Northbound lane). There was also another vehicle that pulled over behind the OPP car for a few minutes, but I didn't ask about that one and am sure it probably isn't relevant to my situation. When I meet with the prosecutor, do I explain all of this to him/her? It seems as though that in the eyes of the law, if speeding is speeding regardless of overtaking a vehicle, then my explanation of the situation doesn't really matter and I obviously was in the wrong. At this point then, I'm not really sure what to say to the prosecutor, but I sure don't want to have a $317.00 speeding ticket, 4 demerit points on my license, and for my insurance rates to increase. Also, I'm not sure if this matters but this was my first driving infraction as well. Any advice, or information on what to expect?