Don't worry about future employers looking up previous jobs if you are not applying for a professional position- they won't and if they do, they can only ask whether you worked at the establishment and maybe the timeline.
Take the job, in the interview process you can mention that you are thinking about school but might take a gap year.
Two weeks before school starts you can come up with any excuse or even just say that the school plans changed.
It appears as if the position you are seeking probably does not have a long training period, which is the main factor that would make an employer hesitant with short-term employees.
College students, including me, work for the 3 month summer period all the time, and employers get this. Even if you mention it to your employer, assuming you have the qualifications and seem to match the workplace vibe, they would probably hire you anyway.