I took the sat subject tests in math 2 and biology for CMU twice. I took them the first time in August, getting a 620 on biology and 640 on math 2. Obviously these are horrible scores so I retook them on October 6th. My question is, should I bother sending them this time if they’re still bad? CMU’s website states that if the tests are a financial hardship for the student, then they will not be penalized for not taking them and their application will be evaluated regardless. Based on my family’s income, this would definitely make sense to them if I were to not send my scores. I am worried that poor subject test scores will hurt my application, and they won’t know that I’m actually an awful test taker. Should I risk and send or just not send? I am applying early decision by November 1st and my test results have not come back yet, not until this friday.
I would not send any score below 700. That said, unless the rest of your application is super strong, including your ACT/SAT, it may raise some flags to not see the subject tests.
So what would you recommend that I do if my test scores are low?
I would not send low scores.
Have a solid list of matches and safeties you would be happy to attend since CMU is a reach for everyone.
Not sending in your scores because they are too low is not the same thing as not being able to take the subject tests in the first place due to financial hardship. If you do not send them in, you will need to be prepared with those other portions of your app. that CMU will now focus on like a laser beam; including an effusive counselor rec. that underscores how you have persevered despite significant financial hardship. 
What SAT/ACT scores are you submitting? If you are an “awful test taker” then are you comfortable with those scores?