Dental cavity treatment examination interval

Went to the pediatric dentist for a treatment, and one molar looked fine on the outside, so I thought it would be a simple procedure. However, upon examination, there was a large cavity inside. It wasn't enough to irritate the nerve, so they didn't do root canal treatment. Instead, they disinfected the inside and filled it.

They tell me to come to the hospital if I get sick, but should I go regularly?

I'm worried it might rot even more.