How to prepare myself to be a software engineer?

I have been a sport programmer using C++ for 4 years, and I can say I'm confident in my algorithm and data structure skills. Recently I decided to try something else, so for the past few months, I learned Python and I really like it, I also learned Flask and have done a small pet project. I'm currently a freshman in a university, I wanted to know how can I prepare myself to be a professional software engineer ?

Here are some things that I consider :

• Work on open sources projects. I'm not actually sure how to do this, since there's a bunch of codes, and I don't know where to start. Do I need to know the projects very well first ?


• Learn new things. I wanted to learn about mobile apps, but I'm not sure whether I should learn it now, or improve my knowledge on things that I have learn

I would appreciate if you could give me some recommendation and the reason.

Thank you.