My heart goes out to the OP 'cause I know how much it sucks getting a speeding ticket (gotta man up though), but the members of this forum are absolutely right. The reason traffic laws carry such heavy penalties is because if we forget to follow them, people get seriously injured, or worse, they die. When you're the only one on the road in the middle of the night at you come up to a stop sign, you're expected to do the right thing and follow the traffic laws. Because when you're that guy going through a 2-way stop sign intersection (instead of 4), you'd expect others to do the right thing and obey the traffic laws so that they don't pull out in front of you and cause an accident.
1. You were doing 20mph over the speed limit. Here in Tampa, anything 15mph over the speed limit and the fine is doubled, so it could be much worse.
2. I hate to say it, but ignorance of the law is no excuse. It's your responsibility to find out what the speed limit is. Secondly, I don't know of many places in the US where the speed limit allows in excess of 55mph that isn't labelled a highway or causeway, so that excuse definitely isn't going to fly.
3. Cops don't have to announce their presence to you. There's a reason why those Ford Crown Victoria's are called the Panther platform.
It's not the end of the world though. It's just one speeding ticket. Pay it, learn from it, and move on.