Med schools don't care about your high school hospital work. You've done 100 hours over 4 years. That's 25 hours/year. Most hospital volunteer programs have you do 200 hours in a year. Even though you've done 150 hours of shadowing, you're still a bit low overall.
I always encourage gap years even if you don't need improvement. You've been in school for 17 years, you're about to be in for 4 very taxing years, plus another 3-6 putting in long hours as a resident. If ever there was a time to take a step back and breathe for a few months, this is it.