Try your best to relax, im just as nervous!
not sure what exam board you have but mine it Edexcel and we regularly have sources so if you have the same board be sure to know a range of sources such as pictures, letter, personal diary entries etc as well as useful questions for me, those 8 marks are hard to obtain, using nature, origin source etc with my board having a good knowledge on your exam/reading skills comes to play really well
Knowing your time periods is vital, my test regularly says them in years such as c.1250-1500 (medieval) don’t get confused as it will jeopardise what mark you get on that question especially those which involve two time periods such as c1700-present (industrial to now)
knowing causes of disease, treatments, diagnosis for each period as well. break them up into fragments so your not as confused such as industrial in the times of individuals playing there roles within society, renaissance the era of rebirth of ideas etc.
these really help with those big 12/16 markers for me, knowing each one. I got taught through an acronym: W.A.S I.T C.C.G
war, attitude, science, technology, community,church & government.
remembering that can help grasp on what you should specifically talk about especially when evaluating.
other than that I’m sure you’ll do great, i wish everyone the best of luck!! hope this helps lol