Carl G. don‘t dispair.
Yes, you should bring your average up if you want to achieve your goals later in life.
Look at the positive side, you are close to finishing high school period, and that says a lot.
I am 28, a full-time federal government employee with a respectable job as a Customs Inspector, taking correspondence university courses. I am slowly but surely achieving my goals in life. I had my first $60,000 year, in 2002. I have a car, and a house, and a cool girlfriend.
I dropped out of high school at 16, and didn‘t even look at updating my skills until I was about 20 or 21, when I started working as a security guard. When I came to customs, I realized I was lucky to get the job to begin with (they had an education clause that was loose, "high school or public service approved equivalent of education and related work experience"). First thing I did was get my GED (high school equivalency). I scored very high marks in that exam. From that I was able to enrol in University as a correspondence student part-time, and that is what I am working on right now.
Life is not lost because I didn‘t finish high school.
That said, do as well as you can, because it will honestly make things easier for you later in life. Having to wait to get into to university until you are considered a mature student will suck if what you want it is to go in right away. You will be climbing uphill all the way.
I now have a lot of certificates and the like on my wall, and am planning to put more there. But I will be honest with you, the one I am most proud of isn‘t my GED, or my customs recruit courses, or any of the skills certifications I have taken. I am most proud of my Civilian Citation, given to me by the Toronto Police. More than anything, I think it speaks volumes about my character, to people who don‘t know me.