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}
{Sender}
