Worried for 'O' levels?

Hi i am 15 this year and my gcse o levels (singapore) is next year around another 360 days time and i really want to do well because my future matters but im just really worried and want to know if this is normal or not? my grades now are pretty bad but i have been steadily improving however i think i need to take bigger improvements otherwise i will not make it in time for my o levels. also when and how should i really start preparing for it?? thanks much people