I am also a new grad RN, graduated last year 6/2015 and have worked at an outpatient office for 8 years. I have applied and applied and applied to CT hospitals all over to get in and get that acute care experience but none have called me back. I have an interview set up for yet another outpatient office and though I am grateful for the opportunity, I was looking to work in the hospital, build up skills set, and build up my resume. I wouldn't be able to do that so much in an outpatient setting.
I think that if you are looking to continue your education into a master's program, working in the hospital setting would be a wonderful experience no matter what unit. And some hospitals do allow you to transfer to a different unit after a year I believe, so don't let the offer make you feel like you're limited to just that position. It seems as if the hospital will offer a lot more for you and your future than the office setting. The sign on bonus is probably a lot less than what the hospital will pay for your courses, so paying that back is just a small sacrifice for what you're getting in return.
In any case you should go to the interview with a clear mind not thinking about any other job but the one they have offered. Make them believe you want that offer and that unit!
I wouldn't pass it up! But this is your decision and you should weigh the pros and cons! Good luck with your interview, review the hospital's mission statements, values and scenario questions! Good luck in your decision!