I think it's fantastic that you are using your practice scores to guide your decision about whether or not to take the MCAT. As long as you see consistent improvement in your practice scores, it should be safe to take the exam. Since you have such a high cumulative and science GPA, this should give you confidence because you do not have to compensate for a low GPA.
That being said, if you are not seeing an increasing trend in your practice test scores, wait to take the exam when you do. Most importantly for you to remember is that the decision whether to take the exam or not is yours. Using the data, you can make the most informed decision.
I don't recommend taking the MCAT if you are also taking classes. You can jeopardize both your GPA as well as your MCAT. I would take the exam when you are able to focus all of your energy on studying for it.
Hope this is helpful!