I just beat the gauntlet. Try to avoid getting hit(duh), as it breaks your chain. Your chain goes up as you kill more fiends without getting hit yourself, and it will boost your points dramatically considering you keep the chain. You can easily breeze past 500 with 2-2.5 minutes left if you keep the chain alive. In fact, I lost it within the first minute but still had 2 minutes left with a new chain. Just keep pressing O and gathering ammo, and you should be ok. The fiends come in patterns too, so if you memorize that, it only helps more.