Currently a sophomore, and I'm starting to realize I don't have that many ECs to show for. I have about 30 hours of physician shadowing and basically very little to no volunteer and work experience. Am I too far behind? Will this be a major issue for med school applications?
OP, you're right to realize you've put yourself in a precarious position. You can turn this around, but only with some significant effort.
As a sophomore with few ECs, you should plan on no fewer than 3 gap years, 1 of which will need to be at an NIH-affiliated laboratory and another as a scribe in a US News-ranked top 10 hospital, preferably east of the Mississippi River. I talked to an adcom member's cousin once and she told me that you need 4 ECs by two weeks into your freshman year to get into a top-27 medical school (research, clinical volunteering, trip to Haiti and/or Albania OR two trips to the sub-saharan region of your choice, excluding anywhere in Namibia, and a leadership position in a culturally-oriented dance troupe of your choice).
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Okay, in all seriousness, I have trouble understanding people who post questions that are this inane and easily answered. What ECs do successful applicants tend to have? They tend to have done research. They tend to have done volunteering in clinical and non-clinical settings, perhaps pursuing employment that gains them further clinical exposure. They tend to have sought out and earned leadership positions. They tend to have pursued hobbies that distinguish them from other applicants and show that they have interests outside of medicine.
Your university or your wider community likely features ample opportunities to check each one of these boxes. You haven't done so yet. So just start. Get off your ass and find a lab/emergency room/soup kitchen, invest some time with each, and you'll be fine. Better yet, identify an unmet need in your community and form your own organization that addresses it.
What doesn't help you is to post questions on SDN that have been asked and answered countless times before, hoping that someone will reveal the heretofore jealously guarded secret formula to medical school admissions. Hint: a generous tablespoon of common sense is the main ingredient.