You should seriously consider taking a gap year, especially since you have zero shadowing hours and haven’t started prepping for your DAT yet. I think you should take this summer to shadow (keep calling around until somebody says yes, or try free clinics) and study for and take your DAT. If you are diligent, you can sign up for your DAT in mid-August and have a good 2.5 months to prepare. Then focus on your grades during your senior year while still volunteering/shadowing. Spring of your senior year, you should focus on writing your personal statement and getting your letters of recommendation. By the time late May/early June rolls around, you should have everything you need. Good luck!