Hi {Receiver} , I know that it was very important that {I am on time/send you the prerequisite materials}, and I’m very sorry for{not being on time/missing the deadline}. I ran into trouble when {reason for delay}. I mismanaged my time and wrongly prioritized other matters over {this one/project}. In the future, I will exercise better organization to ensure that I am more punctual. I’ll also make sure to keep you up to date on my status in case I encounter any unforeseen difficulties. If you can offer additional insight or suggestions as to how to improve my punctuality {on projects}, I am willing to listen and learn. You can reach me at {phone/email}. Sincerely, {Sender}