I have just filled out the paperwork on mid-term alerts- they will be sent out tonight. Just so you know, I took your average homework grade and your exam grade (including the 'supplemental' exam) and averaged them- if the result was 65 or less, I sent one out. You should have enough information available to you from e-gradebook to determine why you got one (or didn't). Performance in the lab is not included in this score.
I am not convinced that one exam and a few homework grades are a reliable predictor of your ultimate performance in this class, but it is all I have to go on.
While I do not actively encourage people to drop the course, I will remind you that the final drop date is 27 October. You should individually assess your chances of passing the course and act accordingly. I am happy to discuss this with people on a case-by-case basis in my office.