Didn't pay attention to rules and created an illegal note card for exam?
Often a professor is no more eager than you to invoke formal disciplinary mechanisms, as they are often complex and time-consuming.  From what you describe, it sounds like you've been given your punishment and find it fair.  If the professor was interested in taking it further, you would likely (but not necessarily) have been informed in the same email.

To find out, you can simply email the professor back.  Say pretty much what you said here: you made a mistake, you find the punishment fair and even generous, and you just want to check whether the matter is now settled, or if you need to anticipate further disciplinary action.

If the professor feels that the matter is settled, and that the grade reduction is all the consequence that you need to face, then you can safely put it behind you; if not, it may become part of your record and may require explanation, depending on how things proceed.