Please guide me. I really need your help. I am very confused.

I am soon to start my second year of college, I am doing btech in CS. And I know python, C, mysql, html, css. That's it. I am more on the backend side of engineering that's what I know.

Can you please give me a roadmap for a backend developer.

Also in vacations I am confused between C++ and java, what should I learn?