This game is too hard. The boss heals himself too fast and levels up way to fast. I get to about 6 minutes and he wipes all my defenses. Then I lose and I repeat the process using strats I learned here but I'm still losing on the first girl. I can't even make it to the second one.
You only need one turret for most of the game since it's basically impossible to kill the enemy until 6 minutes on or so. The strat is to always upgrade the bed when possible, then upgrade the door if you can't upgrade the bed, then upgrade the turret if you can't upgrade the door. Once you get to 5 minutes in you should have a powerful enough economy to fill up the rest of your slots with turrets and go ham.