Getting volunteer hours and medical experiences during gap year can help you, definitely. However, your primary application (where you lists all your activities) will open up in June 1st, and you'll want to submit them by around mid-July at least (earlier the better). Will you have your activities/volunteering started by then? If it began, then you can list your projected hours, although I'm not sure how will Admission committees look at activities that had just begun. It probably won't be viewed equivalent to activities that have begun years before. If you can't get those started, then you'll have hard time filling out on the activities section. Yes, you can update AdComs throughout the application cycle, but not all schools will permit this. You're risking your app being thrown onto reject pile even before you had a chance to update them on your activities.
Summer internship with shadowing/etc sounds fine - but keep in mind you can only assign one category to your activity. Is this going to be a shadowing? or a research? I'm very sorry to hear that you had a difficult time during school year, but committees won't take that as an excuse (although you can certainly try to explain in secondaries). Also, activities in high school won't count. AMCAS want activities you started since college, not before, unless it began during HS and continued into college. Was your shadowing/independent studies with a doc in HS the same doc/surgeon you had your internship with?
In summary, excluding HS activities, your volunteering is minimal, nonclinical is nonexistent, other ECs are minimal, and only exposure to medicine so far (after HS) was with surgeon in a summer that was quite brief - 2 weeks. Great GPA and MCAT will help, but without ECs to back you up, I still don't think it's a good idea to apply this year. You can definitely continue volunteering while you wait for that interview, but that interview might not come to you.
I have no clue what clepping class is.