The other two solutions have solid advice, but some of us just aren't that good. If you're like me and want a solid 200/200 on this game but just can't get this achievement legit (and if you have plenty of free time), there's a way to make it a whole lot easier.
On the last room of the second tunnel, crouch directly in the middle of the room (your bullets should be hitting directly below the target) and just keep killing stuff. Don't exit, just keep crouching and pushing A as fast as possible. The time will run out and you will die, but for each full run (from the time the clock resets until it runs out), you will gain about 80,000-85,000 points - enough points to give you +1 life and a little over. Repeat this long enough, and you can get as many lives as you need to beat the game.
I did this for about two hours and got up to 15 lives... plenty to beat the game with and get the achievement. Like I said though, it will take a lot longer and your hand will be killing you towards the end, but it makes the achievement so much easier.