First of all, a masters without working experience is really counterproductive.

Secondly, are you a female without NS?

Thirdly
1) This is just an annual increment. Polytechnics are statuary boards and you should know that they have a salary guideline to follow.

2) Depends. You can try to find a better offer elsewhere.

3) Read your contract carefully to see if there are any penalties if you leave before the contract ends. Otherwise, just ask your HR.