HI, 

Since youll appear in march 2019 for your 12th finals, you can register for CA foudation by april or so , enquire in your nearby CA foundation course classes , if you do so before June 30th 2019 , you would be elligible to take up the CPT exam in month of november 2019. Or else you can register before december 30 2019, and take up exam in may 2020. 

Good Luck.