This link explains the "SMCs", which stands for Senior Military Colleges, with links to all six colleges.
https://en.m.wikipedia.org/wiki/United_States_Senior_Military_College
You can also Google "Junior Military Colleges", those are two year colleges similar to a community college but with a military environment.
For the service academies, West Point is Army, Naval Academy is Navy and Marines and Air Force Academy is Air Force. Do the research on each, all three have websites that explain admissions requirements.
You do need to raise your ACT score. There's another test in June. Sign up to take it.
Your mom suggested a military college for you? Sometimes parents know their kids better than kids know themselves, simply because parents have twenty plus extra years of more time on this earth to gather life lessons than the teenager. However, I am wondering WHY she thought it might be good for you? Is it because you are you spending too much time with friends and boyfriend, instead of concentrating on school? If your mom suggested a military college to try to get you away from your "crowd", that's a pretty bad reason to join any branch of military. You are the one that will be doing the training, getting deployed - so YOU need to want to be there.
Perhaps a better option is to look at a state college that is not local to you, (that you would stay in a dorm instead of still living at home), where you could work on your grades for a year while researching the service academies and/or military colleges.
You also really need to take some time and research each military branch. I hate to say it but if you're intimidated by PT, the Marines might not be the best choice.