When you apply to a college they request that you have your high school send in your official transcript, that has all your grades (per class,by semester or quarter) since fresh year.
And ALOT of things play a role in college acceptance; SATs, GPA, activities in and outside of school, essays. If your cumulative gpa is above 3.0, preferably 3.5 you can get in at a "decent" or above decent college. Ivy league may be out of reach. Community colleges accept basically everyone. Try your VERY best senior year because really schools only see grades from fresh, soph, junior year when u turn in ur app... maybe a little of senior year.
College look only at the 9th-11th grade grades when you apply early. They are most forgiving toward freshman year and look at junior year the most. A positive, upward trend is a good impression. If you apply regular decision they will probably look at your 1st semester senior year grades. Don't slack off senior year or they might rescind you.
If you have good test scores you should be able to get into a decent college. You probably won't get into a top 50 or maybe even top 100 school unless you did something really amazing. You can always transfer or go to another school for graduate school if you don't get into your top choice undergraduate school.