Yeah even with the werewolves and slimes it's mathematically impossible to win.
The MC has 20 health and the werewolf does 2 damage every time he attacks, which means the MC is defeated in 10 turns (defending does not lower the damage taken).
The werewolf has 12 health, but the MC only does 1 damage, which means the werewolf would be defeated in 12 turns. So it's always a loss for MC at level 1.
You need to increase the damage/health of the MC or decrease the stats of the monsters, so that winning is actually possible. The game's direction is fine, you just need to adjust the numbers.