So I got a 3 on AP Lang when I definitely thought I got a 4-5. I was very confident on the FRQs and MCQs.
If I ask for a rescore what are the chances that it will actually improve my score and are there any success stories out there?
Close to zero.
Yes, but I have only heard of one or 2. Also note that your FRQ score is set in stone; it will not be rescored. But if you have the $30 to spend for peace of mind, go for it, but expect no change.