@ Ms. Anita, I Can't answer your question in a single line. If you already Decided to drop CA, than after that you can...if GST is your preferred area.
But, I think you can do CA, as you already passed CA inter, So, remain is just CA final, There are many others factors also needs to be considered before any decision like your future prospects, Age, economic conditions, time, your core areas, family support, other opportunities ect. Ask yourself, what's your dream, future. You can or can't, ect....and then decide taking into account all other factors.
I think you can clear the exam by little more effort in the same path will give you fruitful results. But choose by yourself, it's you know about yourself better, than others.
In my view its better to continue your CA since you have crossed more than half a way. After CA you are eligible to practise GST. Any as said my Mr. Sager Patel its your life and future. Write down the problems continuing CA. Jot down that can be overcome by yourself. Wish there is no problem in continuing your CA. Good luck