Your teacher possibly noted whether the mistakes were bad or not so bad ones. Maybe you occasionally were able to tell from the corrections what the teacher expected of you, becuase he noted the correct wording. Your partner will not judge you by them, as his or her corrections are only there to help you learn. You yourself determine what is corrected and how your partner should do this for you. Besides, your partner also makes mistakes and expects to receive corrections from you.
Mistakes are an important part of the learning process.
However, each mistakes can only help you if it is brought to your attention and when you are able to stop making it over time. Still, it is best to ask your tandem partner to bring your mistakes to your attention.