Irrespective of whether or not it hurts you for medical school admissions, play the tape to the end. If and when you get to medical school, the academic rigor of the hard sciences becomes overwhelming very quickly for pretty much everyone. Trying to piecemeal your way through them is a tactic that will only get you so far.
At my school, a single lecture on a topic like bacteriology encompasses the most important information about the discipline that you would normally only come into contact with in the context of an undergraduate course at the very end of the semester, once all of the introductory content has been presented, tested, and applied.
In medical school, they just expect you to either already know all of it, or fill the gap yourself... which of course you need or else you rote-memorize everything and those isolated factoids have nowhere to live in your brain, and ultimately are not retained over time and cannot help you reason through questions.
Ordinarily, you'd think, OK, I can spend a day doing the best I can to fill in my bacteriology gaps. But there is more than one lecture per day.
What do you do when you are presented with the coagulation cascade to memorize and guide treatment decisions and you've never seen hemostasis as a concept before in your entire life? Same for pharmacology, embryology, and histology... all at the same time? You only have the same 24 hours everyone else does. With anatomy it's usually not even enough to sit at your computer for many hours trying to memorize what hole goes where, visually. But you have to find the time or you fall behind.
And just when you think you've survived that week, the next comes, the topics are totally different, and you're just expected to continue playing catch-up for pretty much the rest of your academic career.
It's good practical advice to protect your GPA, but I think it is poor long-term advice. At some point, you have to give yourself the opportunity to see real rigor without handicaps you create for yourself. I'm not saying take 4 hard sciences in one semester, but you should really consider challenging yourself with content relevant to your goals while you can still control your workload. One at a time won't get you there, and you are running out of time if you do not plan further education beyond your baccalaureate degree. Just my 2c.