What was your math score on the SAT?
How do your grades (both overall and in math and physics) compare with others in your high school and in your country? I have some experience as an international student at two of the universities on your reach list (and was admitted to a third but did not attend), but I do not know anything about typical grades at high schools in Singapore.
Generally in my experience admissions at top universities in the US do have someone on staff who understands the grade scales used in other countries. Thus your grades will be interpreted in the context of the education system where you are studying.
Be aware that the top schools in the US, including the ones on your reach list, might be considered “more academically demanding” rather than “better”. As examples, studying at either MIT or Caltech has been compared to drinking water from a fire hose. You need to work very hard at these schools, and the desire to do this needs to come from inside the student themselves. Personally I was more ready for this when I was in graduate school. Different student react to this in different ways. Some love it, some hate it, and some love it part of the time and hate it part of the time. Again, you need to want to do it.