Am I too late? Thinking about PhD in my third year.

[confused_conure500]

I will be graduating in May 2026 from a T100 school in the US. I am a Math+Computer Science double major, and throughout college I've been trying to become a competitive applicant for a PhD in CS. However, as I've gone through school, I've realized that I like Math more, and I'd like to look into PhD programs in algebraic geometry or linear error correction.

Overall GPA: 3.7 (This will become higher, as I absolutely grind my classes. I am confident I can get this to a 3.8+)
Math GPA: 3.65 (Again, I am confident I can get this to a 3.8+)
CS GPA: 3.9
School: T100 US
Research Experience: DoD Mathematics Research Coop, compelling research in linear error correction (upcoming)
Teaching Experience: Student Instructor and Grader - Discrete Math (1 semester so far, will likely continue unless I mess up)
Awards: Dean's List

I'm a white male US citizen, native English.

My main concern is letters of rec. I can get 1 very strong letter from a professor I will be doing research with, as well as taking multiple of his graduate level classes and being able to keep up. I believe this letter will be very strong. 1 ok (better than did well in class, but did not research with professor) letter showing my determination. I'm trying to forge more relationships with professors to get a 3rd letter, and I could possibly ask my boss at my coop.

I'm also coming into this quite late, and I really don't know what to do. Many people say to take the GRE, while others say to not. I also am not nearly as well versed in math PhD admissions as I am in CS PhD. However, the more time passes, the more I realize that perhaps this is the path to me. CS is interesting, but the higher I get into math the more I want to know. What would you all suggest I do to optimize my chances? Is it worth it to keep going, or should I just stick to CS?

[juicetrainwreck]

What do you want to do?

You don't have to be in school to learn mathematics.

[confused_conure500]

What do you want to do?

You don't have to be in school to learn mathematics.

I am very interested in advancing a field of science, whether it be computer science or math. I understand your position, but grad school is a non-negotiable for me, even if I need to take gap years or do a masters to make it happen.