I took the SAT for the first time in March and received a 1340. Then I took it in June and now have a 1380 superscored. Should I take it again in the fall, or does taking it a third time look bad?
Take it as many times as you need or want! I think colleges only see the score you submit to them unless they are granted access to your other scores. Even if they do, it won’t look bad to keep trying to improve your score 
I think if you want to continue to improve your score, you should go ahead and try!
Colleges usually recommend students take the SAT 2-3 times so if you feel like you could do better go for it!
Some colleges DO ask for all your scores, but fret not. You can give the SAT up to 5 times, though I personally would not risk more than 3. What’s going to be important to colleges is whether or not you are progressing with each SAT. They do not want to see miniscule increases, and most definitely not a decrease, so only retest if you’re willing to work hard and boost your score by 50-60 points.
personally i would take a couple practice tests under timed conditions and see if your score increases. If not I wouldnt waster your time
Perhaps you should try the ACT. Some students score better on one test or the other.