Really? Tried it again, and worked for me. You just got to make sure to protect your line of badgers with 2 slimes in front of them (2 slimes kill 1 red fireball). Once you have 3 slimes guarding your four badgers, build that top row starting with a 5th badger and 2 slimes.
If that doesn't work, maybe just be quicker dropping those badgers at the start. Not sure how else to explain it.