What should I do??

Perhaps you can meet with the instructor and review the questions that were marked wrong that you believe you got right. As far as wasting your time by going.......to school you mean? How is it a waste of time? You're learning, aren't you?

Scantron scores aren't usually wrong. If you think his answer key was wrong you should ask him to review your score with you.

I am surprised your prof didn't tell you that before your first test. Most of them have white-out on hand so you can cover up erarsed answers. Usually they will look over the scantrons to check for that anyway. I'd definately ask to have your test re-checked .

In my class, a student said the exact same thing you did. She said she knew she only got a certain # wrong and not the amt the prof. said she did. She met with the prof and turns out she mismarked them on the scantron. She was off by one and so although she had marked them correctly on the test sheet, the scantron showed different answers. Did this happen to you?
Also, if the scantron machine is marking them wrong, then all you should have to do is go to the prof and ask to see your scantron sheet and compare what you marked and know is the correct answer to what the scantron says are the right and wrong answers and then you'll know if the scantron machine messed up.