Assuming you already know US History:
https://www.amazon.com/History-Course-Online-Advanced-Placement/dp/073861226X/ref=dp_ob_title_bk
I read the REA APUSH Crash Course book in ~3 days. It only has the most important details (so it'll be missing a couple things from AMSCO such as nearly every battle, for example), but it's really concise and a very fast read. Getting the eBook version would probably be better to not have to wait for shipping since the test is in less than a week.