At the moment there is very little chance (but not zero) of becoming an astronaut. Studying engineering (don't do a pure science) may give you a chance of becoming an astronaut.

However if SpaceX is successful in building a fully reusable spacecraft (starship) there may be many more opportunities in becoming an astronaut, as space flight may increase dramatically.

So study engineering and other things that may lead to becoming an astronaut, even if you don't you will have a good career to fall back on.

Good luck.