There are v. few actual state laws or regulations that keep you from working in a position "lower" than your level of licensure (I know that my state has no such law/regulation, however, some other posters here have mentioned that it is specifically prohibited in their state), but there are legal and professional concerns. My state BON has issued a specific statement saying that it strongly discourages nurses from doing this because of the professional and liability concerns.
The problem is that your employer
will tell you you're not allowed to do anything beyond the job description of the position in which you're working (lower than your level of licensure), but, if anything goes wrong, wrong enough to end up in court, the courts
will hold you to your highest level of education and licensure, regardless of your title or job description at the time. Many employers
simply won't hire people to work in a lower level position (below their licensure) because of the liability conflicts/concerns, and many employers who will
do so are doing it because they don't mind exploiting you (basically, getting an RN for a CNA/MA salary).
I understand that times are hard and jobs are hard to find these days, esp. for new grads, and I'm not saying you definitely shouldn't do this -- I just think it's important for people to understand the ramifications and potential risks of the situation when making a decision about doing it. I would also strongly encourage you to carry your own professional liability (malpractice) insurance, if you don't already. If anything does go seriously wrong and your employer can find a way to blame it on you, they will do so in a heartbeat.
There are some other threads here on this same topic, if you want to look for them and read further discussion. Best wishes!