My SAT score is nearly 300 points lower than my PSAT score. What happened?!?

took the SATs for the first time a couple of months ago, and I am shocked by how low my scores are (specifically in math). My SAT score was 270 points lower than my PSAT score, and math accounting for 240 of those points (I got a 420)! :( I was flabbergasted considering I usually do the best on math (high 60's on the PSAT). I came out feeling as though I did much better than my score indicates. What does this result entail? Obviously I need to work more on math, but it just doesn't make any logical sense :P Could I have possibly made a bubbling error, ergo messing up my entire math section? It was not even close to my writing and critical reading scores.