(This is not a question of whether C++ is worth learning / dropping)
My high school offers three levels of programming. I took the first on this year, which was on C++. The next two courses are on Java. (why would the put C++ first then java, isn't java easier to learn?)
Would it be more effective to just drop C++ for two years, or because the courses move at a slower speed than what one can learn on their own just continue C++, while staying with the class (I am still surprised how similar they are).
I see really no reason why you couldn't try learning both languages at once if you wanted to. otherwise learn whatever language you are more interested in. There is no one best language. If you want to be a programmer you should know a handful of languages.
So give it a try and if you find that you are getting confused learning both at the same time just pick one that you like the best and go with it. Though personally I would stick with the high school course since it might help you with enrolling in a good college if you plan on going to one.