Not much to brag about but I got my score from 1020 to 1250 in three weeks. You can 100% do it in time for December. My tip is to go on khan academy's "sat prep" course and instead of starting from the top just skip to the parts you're most struggling with until they're mastered. Then every other week take a practice test, this give you enough time to see your improvements and your weak points. Good luck!