No need to be embarrassed about your experience. The recruiters at job fairs are there for two reasons. The primary reason is to fill open positions. The secondary reason is to advertise their companies (in fact, some companies will go to job fairs with no open positions so as to simply have a presence there).
Now for the ones that are trying to fill open positions, this is an ideal time for someone such as yourself, who is unsure about your qualifications, to go talk to the recruiters and ask questions. Let them know what your experience is, what your aptitude is (i.e. if you're good at dealing with people, good at learning new things quickly, like working the night shift, stuff like that which may not be reflected in your employment experience).
So you talk to a recruiter, let them know about you, and find out more about the positions they have. If the recruiter encourages you to apply for a position, take an application and leave a CV (If you have one), then move on to the next recruiter. If you're not qualified for any positions that a recruiter has to fill, thank them, then move on. He or she is not going to look down on you in any way.