Sounds like it may be better going to dual, but it depends how much effort you are putting in now, if you are slacking then get your head down and revise, there's no reason why you can't stick with triple.
It also depends what you want to do in college (if you going that is). I only did dual, and went on to do AS Biology and AS chemistry. I ended up dropping Chemistry because I didn't get on with it. Doing triple if you plan to take them onto college will definitely give you more of a benefit than if you do dual before taking them at college.