I think it's a great idea to do some self-study this summer, hopefully you'll do your major in CS aswell :).
As to the advice I can give: Don't condition yourself on "learning a programming language", that's a mistake everyone does in this field. Because learning the concept of programming and what how things actually work in low-level (hardware) is the key element to being succesful on whatever comes next. People who don't learn the building blocks first, start to struggle later on when things get more an more complicated. Yes most of them can write code, but there's "good code" and there's "shitty code" :), those people can't code efficient software and usually work lame IT jobs when they graduate.
When you've achieved that, you will be able to learn a programming language in weeks, because the main idea behind all languages is the same exact thing, it's just a different way of interpretation. Every single device we use is actually the same thing whether it's a Computer, iPhone or Android. They're actually all called one thing: "Turing machine", just a little more advanced.
I hope I gave you the main gist of it all, I can reccomend Khanacedemy, some of their lectures on Computer science are great to begin with. Check out Hour of Code: https://www.khanacademy.org/hourofcode It may look silly but believe me it's actually very very important. Yes it might look very basic level, but trust me you should take it seriously.
When you decide to get to the real deal: https://khanacademy.org/computing/computer-science/algorithms Understanding the logic behind algorithms is one of the building blocks I mentioned earlier. By the way I should warn you, if you don't like math, start liking it now :D. Or you'll struggle a lot along the way.
Finally, don't take my word for anything I just mentioned, remeber that I'm giving my point of view of things and not experienced enough to be taken seriously for anything I say :) Always do your own research as well!
If you have anything specific to ask don't hesitate to pm me again! I'd be happy to help!