In the grey zone

So,

I am a recent graduate from an RN program, still waiting to take my boards. I received a job offer from a large local hospital that I "accepted" but will not start until Jan. 10th. I had previously applied for another position closer to home (before applying for the position I have now accepted), and was offered an interview last week, which I accepted. After the interview, I truly feel the second position is the one for me, and I would really flourish as a new nurse and have the support I will need, which was a concern of mine at the first position at the larger hospital. My question is this: If I am offered the position closer to home that is the better fit for me, am I being extremely unprofessional by accepting? Will I be burning bridges with the larger hospital to turn down the position after I've already accepted it? I have done a preemployment physical for the verbally accepted position and some online paperwork but not signed anything or been to an orientation. Any advice would be much appreciated!