Section 4 and careless driving?

HELP! While out to pay respects to a dead college, I was involved in an incident with another motorist. The car in front stopped at some roadworks ans then the light changed green. I followed the car for around 100 yards when it stopped to let traffic from the other side cut across. I hooted my horn to let the driver know I was behind yet when the car moved, I was subjected to a torrent of hand gestures. After around 200 yards, I over toke the car and the barrage of hand gestures continued. I stopped the car walked towards the other vehicle and punched the side window 3 or 4 times ( didn't break the window). I then realised that Id done a terrible thing and walked away avoiding any more confrontation and continued my journey home. Im now charged with section 4. didn't hit or hurt anyone (I never have) and know im told this could be a custodial sentence that would certainly end my career, lose my home etc? admitteded before arrest that I overtook the other car where shouldn'tnt off and hit the window. They have 4 witness's including an off duty police officer! how bad is this an am likelyey to go to prison. My first offence.