When asked why you're going to the US during your F1 visa interview, it's essential to focus on the educational aspect. While your desire to start a tech company in your home country is commendable, the primary purpose of the F1 visa is to pursue higher education. Therefore, it's best to emphasize how studying computer science at University xx in the US aligns with your academic and career goals. Highlight the program's quality, research opportunities, and exposure to cutting-edge technologies. Mentioning your intention to apply the knowledge back in your home country can be an additional point, but remember to keep the main focus on your educational aspirations. Good luck with your studies!