There are generally three kinds of undergraduate courses in Singapore according to your situation. If I didn't apply with my college entrance examination results (I came to Zhejiang in 2009), my junior college entrance examination results should be around 670 (10), or at a university (about 25 universities in China have an agreement with the National University to select several outstanding students every year) (SM3), or come to Singapore to study for A level and re-take the college entrance examination here. As far as your situation is concerned, first find out whether there is an SM3 program in your school. The school should have informed you at the time of selection, but it seems to be the first half of the freshman year and it should be over. Don't prepare for the college entrance examination unless Gao Fu makes up the exam, which is not realistic for you.

Suggestion: It is a waste of time for you to re-prepare for the college entrance examination. I suggest you go to college first and work hard by yourself. I think we can try the SAT, go to college in America and transfer credits here, but the autumn transfer has passed. You can prepare for SAT and TOEFL in summer vacation and transfer in spring. If you want to go to NUS with all your heart, come to graduate school. There seems to be few precedents for our school to transfer undergraduates to other schools. But the requirements for graduate students to come here are also very high. If the school is not very good, the GPA must be high. Science and engineering students should have scientific research achievements, and literature and business students should actively participate in the organization of large-scale activities. The resume here is scary. Therefore, if you have this goal, you can consciously cultivate all kinds of qualities to get close to the goal.