Awful dream that I was still in high school and had to take standardized tests online. I was still exactly the age I am now but I apparently hadn't finished high school? Wow okay then.
Ow! I hate those! Is your brain telling you something? Would you like to do things differently if you could go in the past and redo them? 
I kind of wish I had taken high school a bit more seriously, although it's not the end of the world that I didn't.
There you go. But it's true. Keep up your current good work, and your high school results will have no impact on your future.
What Stereo said. Stress dreams are unique to the individual, but a LOT of us have them about school.