Do you think it's bad if I throw my lab partner under the bus?
Why would you want to throw your lab partner under the bus?
I made some mistakes on our lab experiments but I don't want to take the blame for it.
You shouldn't blame someone else for your mistakes. You need to accept responsibility for them and try to improve your work going forward.
I don't want to take the blame, I'm going to tell the instructor my partner made the mistakes.
Blaming someone else for your mistakes is wrong and you'll feel very guilty if you do that. Just accept and admit that you made the mistakes and focus on improving your work going forward.