Free advice from someone who's been at this for a while: when you realize you're going to miss a deadline, send an email to the person you promised the thing to saying "hey, I just wanted to let you know I'm going to miss the deadline."
I know that's a hard email to send. But you need to.
95% of the time, it will turn out that the person is actually fine with you missing the deadline. And the other 5% of the time, you will still be better off than if you'd said nothing at all, or waited till the last minute. The sooner you tell the person that, the less upset they will be.
Pull off that band-aid. Send the email.
I am aware that the above is me veering dangerously close to "LinkedIn Enthusiast" content. Don't worry, the dick jokes will resume shortly