I understand that you're worried about that semester. I am worried, on your behalf, about your MCAT score. If you put any energy towards worrying about your undergrad GPA or that one semester instead of putting energy into getting a competitive MCAT score, then I think you are making a mistake.
A 3.4 is not a bad GPA, and you are not the only one who had a bad semester.
Can you/someone comment on my terrible GPA/ spring semester where I essentially withdrew from 3 classes and got a C+ in the other?
You'll have a chance to explain it when you apply. Every med school's secondary app has a place where you can comment on academic anomalies.
Should I retake undergrad classes,
Only retake prereqs if you got less than a C in them, or if you didn't learn the material. Only retake other classes if you're applying DO. Otherwise, retakes are no better than new coursework, from a GPA perspective. A retake does nothing to demonstrate academic prowess, nor does it undo what happened in the past: that semester has to be reported as it happened on an MD or DO app.
take some grad-level classes at a local college
Grad work does nothing whatsoever to address undergrad GPA. Doing an SMP is an exception to this, because an SMP is specific to med school preparation. Your GPA, imho, is too high for an SMP, and an SMP will not absolve you from an MCAT retake.
That said, if you sign up for a 2 year masters in biomed program at a DO school, you may be able to get away with not retaking the MCAT in getting accepted at that DO school.
or enroll in a formal masters program?
Why? Are you interested in studying a subject at a grad level? Being interested is a good reason to do grad school. Wanting to go to med school is no reason to do grad school.
You haven't listed "take more undergrad" in general. The prereqs aren't the only science classes. There's a whole world of upper division undergrad science you can take (all of which is helpful on the MCAT), such as microbiology, genetics, physiology, neuroscience, biochemistry etc.
I really dont want to do a full post-bac and retake allll my sciences.
If by "postbac" you mean a program where you do the prereqs, such as Bryn Mawr or Goucher, you're not eligible. Because you've already done the prereqs. Again, retakes are only advantageous for DO school and only required if you got a C or lower.
That said, if you didn't
learn the material in the prereqs, and that's why your MCAT score is low, then what choice do you have but to relearn the material?
I just want to plug up issues in my app.
MCAT MCAT MCAT MCAT MCAT MCAT MCAT.
Im planning on retaking the MCAT either this April or this summer and apply again this or next cycle. Either way, I will have some more gap years ahead of me..
What are you doing to prepare for a successful retake? I suggest that you should be spending a few thousand dollars, and dedicating several months of almost full time work to it. I suggest that you should not retake the exam until you have beaten your goal (which should be 32 for MD, 28 for DO, these are the averages) on multiple AAMC practice exams. You can get MCAT-specific advice from the MCAT forum.
Best of luck to you.