How do I get this, please? I finished a game all the way through, grabbed all the special ammo, destroyed all the ships and didn't get hit once. However, I only got a score of 3950. What do I need to do to get the right amount of points?

Its a tough one to get. I had the same problem back during the plot. I accidentally got the achievement after several rounds of "perfect" games and not getting it, so I'm not completely sure what happened to get it since I wasn't paying attention anymore, just assumed I would never get it.

Part of it is luck - the ships you randomly get are worth different values, so you need to get just the right selection of shps.

The second part, I think, is that if you hit and hold the right arrow key, you move a little faster and if you can manage to do this throughout the game, you can get a higher score.

I started playing this during the plot, liked it a lot, so kept playing. Finally, after all this time, I got over 4500 yesterday. During the game I missed a ship and hit the left arrow key to back up and try again, so it's not playing a perfect game. I've also noticed it takes 3 shots to blow a ship if I take my finger off the right arrow key and 5 if I keep it on. My score has never depended on how many times I fire. I THINK it all depends on the ships that come at you. Those little ones are worth 100 points so the more you get the higher you get. A few days ago I got 3 of those that were too low to hit and my score was 3900+. I would suggest just keep playing and sooner or later you'll get the 'good' game that gives you the achievement. Good luck!

Hmmm based on info, its possible that if you use the left arrow key and slow the game down, you might get more ships, and get a higher score that way? Experiment, try different things.