The best answer I can offer you to continue to improve your grades, your course rigor, your test scores and intellectual vitality to the best of your ability. Your grandfather will/would be more impressed and happy if you did this and focused on being the very best version of yourself rather than focusing on getting in Harvard College.
What 99% of high school students and parents forget too often is that higher education should be life long process and not something that begins with the college admissions process and ends with the college acceptance letter.
So you need to stop worrying about where you get into college and focus on being a better smarter, kinder, compassion human. Because in the end, that will define you and your work and legacy you leave behind, not where you went for undergraduate college.
Going to to Harvard doesn't mean you are better human being. There are at least 10 people I can name on both hands that went to Harvard that I think are terrible humans. And Harvard would agree that it can't be responsible for the actions of those it admits nor those that drop out or graduate from Harvard. Harvard is only a great school if you are great human being to start with.
We as a society have to be more intelligent about why we think one school is better than another school and it should NOT be because of clout, prestige or political influence. While it's true that many Supreme Court justices have gone to either Harvard or Yale, it doesn't mean that they are very smartest or best humans that current or future Presidents can pick from. It just means the system is sort of rotten from the core and antiquated and needs serious reform so we can have the very best humans defending, and augmenting the living document called the Constitution, versus those that were appointed by partisan Presidents pushing an agenda.
Therefore, I think your grandfather who was mentoring you would agree with my point of view that all that really matters is what kind of person you grow up to be, not where you go to undergraduate college.
So do your best, and if your best is State College or small competitive liberal arts college, that's certainly good enough for anyone. And if you have higher aspirations to be a Supreme Court justice or Medical Doctor or CEO, you can always apply to Harvard Law or Harvard Business School or Harvard School of Design, or Harvard Medical School. It matters where you end up, not where you start.
But whatever you do, don't spend the next 3 years of HS thinking that if you don't get into Harvard, you will be a disappointment to yourself or your grandfather. 97% of applicants do not get into Harvard, and 95% of Ivy applicants do not get into Ivys. Are these students all losers? I would never think so. When you understand how un-meritocratic the private colleges admission system really is, you can not think this way whatsoever. If someone gets into Harvard because they are a recruited athlete, a legacy, a faculty brat, or just super rich because their parents had $10MM to donate, are these people better than you? If someone gets into Harvard because they are a hooked applicant who is Black, LatinA, Indigenous, Low income, marginalized, or first gen, are they better than you? If Harvard only used Merit criteria like test scores, intellectual vitality, grades, course rigor and ignored all the other 100 data points, I think it would be better for the world. Still 1/2 the applicants would call foul somehow, but at least it would be fairer than the current benchmark of fairness.
Good luck.