Professors sometimes get emails from students who don't know the best practices for contacting them. You received this page because you sent a message with one or more of the following issues:
If it's your first time learning about these practices, there is no need to apologize to the professor. There's also no need to resend your email, as long as the professor understood it. Just follow these practices in the future.
For other faculty: I've intentionally written this page in general terms. If it's applicable to your interactions with students, you're welcome to use it when replying to student emails.