I try kissing her but she refuses she always say not now and I keep asking my self when
Kissing is a super-romantic thing, with the right person at the right time. Therefore if your gal is not ready to do it then is important that you respect her decision. Relationship is about open and honest communication, you could find out what her concerns are and the time she thinks she will be ready for a kiss.
In the meantime check out this article on kissing: https://lovemattersafrica.com/making-love/kissing-top-five-facts