Honestly though, human mind can't remember things with such short amount of time and while being stressed out. So the more you cram now, the harder to remember it all.
That being said, keep repeating bits of info you need to learn while you do every thing and anything (don't think of it as work but more like subconscious thoughts). Teach other or record yourself talking can trigger other part of your brain and help with memorising. And try not to stress yourself out and have a healthy schedule to keep your brain at its best.
Other than that unfortunately I have no tips. My friends who take History are diligent and passionate, so they rarely ever have to cram.