I need some tips for 200m?

I am a 100m runner aged 13, and i can run the 100m in about 12.4 on gr, probably around 12.1 on track. However, for my scottish schools athletics, i have been entered only for 200m. This season, my times are around 26.6 on gr, but i really need to run it in about 25 seconds. I dont have much time to prepare, what should i do