To help you with this journal entry, I'd talk about the risks of obtaining a STD from unprotected sex and all of the health risks that come along with an STD.
Although, most focus on the STD part, it wouldn’t be a factor AT ALL If protection is used. This would also prevent pregnancy. But, your question focus on not doing it at all. Having sex while being a teenager can have mental impacts. This is often unconsidered, which it should be talked about more often. Plus, it’s illegal for minors.