Thank you, looks like i played it completely wrong
I strongly suggest running away from the single Bug enemies on the very first map when Ben is solo, but then pushing through The Bridge and outside the Cavern to get inside the Cavern to the waterfall room. Then grind up to level 4 or 5 while near the healing save statue.
Run back to the house to rest if necessary before you get Sunny. Also have to go home to learn the girls' PowerSkills from the plants you get in Sunflowers Meadow before taking on the boss battle there.