Lukas, you're what, 16 right now? And you're having a lot of info thrown your way by guys with myriad experiences in their respective "big" military branch and SOF units as well. Start reading here and letting the information sink in before making posts that would be viewed as the 'knee-jerk' type. I lurked on this site for 6-8 months before I signed up. The mods/admins/vetted guys don't say "read more, post less" to be ass holes. Do your research. As a junior in HS who wants to go to college first, you have plenty of time. Right now you should be focusing on grades and enjoying your last 2 years of HS. If that means drinking, partying, playing sports, going to church, hunting, fishing, whatever it is...do it! I think many of the more experienced people here would echo that sentiment as well.
As far as a back up plan, any time you DOR/Med. drop from a selection course you will be left to the needs of XYZ branch. The job you want might not be on the sheet the classifier hands you. When I DOR from mine, I had about 16 job choices in front of me because I got a 99 on my ASVAB. I wanted Crypto...guess what, wasn't an option. YMMV. Again, you have a lot of time in front of you.
I hope this helps some.