Use dot patterns. It worked a treat for me.
Basically you want to reduce the essay down to something like this:
...
..+.
...
..++.
..-
...
....
Thats a 7 paragraph essay with three stats, one quote, 3 sentences in first parra, 4 in the second, 3 in the third etc.
Much easier to committ to memory.
Once you get into the exam, draw out the dot pattern, write down the stats and quote, then the topic sentence for each paragraph. You will remember the rest from that essay outline.
Come up with your own variation but basically you want to create a legend for content with dots, dashes or plus signs... that way you have a visual road map of the structure you have planned.
Most important thing: read the fricken question and make sure the essay you have prepared answers the question asked of you.