You definitely need to take more classes. I've learned from applying and not getting in that what gets you in dental school are your stats..GPA and DAT. Extracurricular, like many have said only helps you so much. Especially since applicant pools are so big nowadays, that almost everyone applying will have similar experiences, it's the GPA and DAT that will set you apart. Schools just want to know if you will be able to handle their coursework, and having a low GPA will only tell them it might be risky accepting you. I know someone with good GPA and great DAT scores with no research, no internships, no volunteer and almost no shadowing get into multiple schools.
It sounds like you don't want to take anymore classes, but you have to suck it up, there are many people out there going the extra mile to get into dental school, working hard and paying their dues. You can't take the easy way out. But if you think taking a few more classes is too much, well you'll have a surprise in store when you get into dental school.