Preschool advice

My sons 3rd birthday is February 4th. I’m hesitating to send him to any kind of preschool until he’s 4. He’s also not potty trained yet and I prefer him to be potty trained before sending him to school. I don’t like the idea of anyone outside changing his diapers. He’s very social and around kids all the time though. Am I a bad mom for not wanting to send him yet?