Hey, I am a junior who used to be quite lazy. I took the ACT and got a 35 overall and a 36 on the essay, but my cumulative GPA is horrible. I go to an IB school, and I think I wasn't too serious in freshman and sophomore year, and that tanked my GPA. Now that obviously isn't an accurate representation of me, as my scores indicate and as I feel. ( I got a 3.94 S1 of junior year and am on track for a 3.75 at least in S2). Furthermore, My highschool gpa has increased every semester, showing a trend of growth. Is there anything I can do to counter act the damage done earlier in my High school years?
As outlined in this article, junior year is the most important year of high school in the eyes of colleges, so it's great that you've improved your GPA significantly. A trend of improvement says a lot, but whether you can bounce back from low grades freshman and sophomore year to attend an Ivy League school is dependent on a few different factors.
If your version of a "horrible" GPA corresponds to mostly Bs freshman and sophomore year, then you probably still have a chance. On the other hand, if you earned mainly Cs or lower across the board during those two years, then your situation might be unsalvageable. The only exception is if you went through some especially tough times and you can effectively explain the circumstances to colleges in your essay or in the additional information section of your application.
Another big factor that will come into play is whether you have anything else going for you outside of your regular academic qualifications. These colleges probably won't accept a student who earned a very high ACT score, had mediocre grades for half of high school, and was minimally involved in a smattering of extracurricular activities. I'd recommend reading this article for more information, but essentially the best thing you can do to redeem a less than stellar GPA is to demonstrate impressive achievement in a certain specialized area.
For example, if you're interested in science, you could aim to have some of your research published in a peer-reviewed journal with the help of a qualified mentor or win a prize in a national-level science fair. If your passions aren't as academic, you might lean towards starting your own charity organization or independent business venture instead. Whatever it is you decide to do, you should aim for concrete accolades and statistics that show the quality and success of your work. I'm not saying you absolutely need to do something amazing to get into an Ivy League school. However, since you're starting from behind with your GPA, it's even more important to show that you're a unique applicant who will make important positive contributions to the community.
Also, a heartfelt, extremely well-written personal statement that gives voice to your struggles freshman and sophomore year can go a long way. You could write about how you managed to overcome adversity early in high school to end up with excellent grades and scores by the end of your junior year. Being able to push through setbacks and get yourself back on track shows great strength of character.