First of all, congratulations on the acceptance! That is a big achievement in of itself and it sounds like you now have a few options. The answer to this question really depends on the type of person you are. Some relish the opportunity of studying away from home and experiencing the independence that comes with it. Others are completely content with the status quo and know exactly what they want. And obviously this is a spectrum rather then two quantitative sides. Now in your question, it seems like you have identified finances as the only barrier here but i would like to point out other ones such as proximity to family and friends, living situation, etc..
In terms of deciding whether or not you should interview at the other schools, i would say absolutely yes! The cost of travelling to UPenn and Harvard and attending an interview is very little when you compare it to the big picture of attending dental school and being in hundreds of thousands of dollars in debt. You may find that the UPenn or Harvard offer something that is more aligned with what you want to get out of the dental school experience. So in short, yes, i would definitely suggest you to attend the other interviews with the security of knowing that you have already been accepted elsewhere. These are no pressure interviews. They will be fun!
Now when it comes to scholarships and bursaries, it is not unreasonable to ask each school about these options. Many schools have programs in place to offer additional funding to students based on various criteria. So do some homework with these schools and find out. Will it be too late in the game to receive additional funds? Perhaps. But you will never know unless you try!
If finances are the biggest deciding point here for you, then it would obviously make sense to simply attend UNC due to the in-state costs but even then, i would recommend you to interview at the other schools simply for the experience. The amount of money you spend attending those interviews will be peanuts even when compared to the in-state costs of UNC dental school.
I hope that helps! Let us know what happens