The H2 Maths syllabus assumes knowledge of Additional Maths at 'O' level.However, schools may allow students who did not offer Additional Maths at ‘O’ level to offer H2 Maths if they show an aptitude for the subject. These students must be prepared to put in the work to bridge the knowledge gap.
Depending on the route you are going to take, either Poly or JC, A-Maths is going to affect you in some ways.
For example, if I plan to do engineering course for my Uni, Maths is definitely a MUST and if you were to do a little research, you will see that most engineering course will require you do have at least a H2 Math pass.
Check out the different Uni entry requirements for A Level results HERE >> NUS, NTU,
Polytechnics offering different courses also have their own admission criteria.
I strongly recommend you to sit down and think through what kind of programmes you wish to further study on BASED ON YOUR INTEREST. Then check out the offerings of each educational instituition.