Okay, I have a differnt take
While you may have been the stand on boat, there are two things that I have issue with that you did, based solely on what you wrote in your OP.
Issue One: While it is not specifically stated, you imply that you were close to or on a race course. Maybe you weren't and the two racers that you state were 300' in front of you were just racing each other. If that is the case, then what I write next is not applicable. If you knew that you were close to two boats the were racing, in race, why not just alter your course and sail around the course, or at least to an area where the traffic is less. While two boats is not real traffic, once they get within several boat lengths and they are engaged, why not give them the benefit of the doubt and get out of their way, stand on or not?
Issue Two: If you're in close proximity of other craft, what is the reason for your using autopilot? I'm sure others with have opinion on both sides, but I think it is a little irresponsible to steer with an AP, especially with very close on coming traffic that is obviously encroaching on you; stand on or not. You basically waited until the last possible second to actually get up and disengage the AP and do a collision avoidance maneuver. What would have happened had you not been able to disengage the AP? You really left yourself no options by waiting to the last second. I very rarely use AP when sailing in an area where there is congestion. I do use AP if I by myself to raise and lower the mainsail, but that is it and it usually takes 5 to 10 seconds and I do it in area where the area is clear.
If you liked my advice/response, give me some rep points. If you didn't......well what do you expect, it was free.