TIFU by pretending I was already doing my degree when I hadn't even finished my diploma

Throwaway because I'm absolutely screwed.

I genuinely don't know what to do right now.

Last year, I was supposed to finish my diploma. I had one exam that I didn't take, which meant I never actually graduated.

The plan was that after finishing the diploma, I'd continue to university and start my degree earlier this year.

Except... I didn't.

And instead of telling my parents that I hadn't graduated yet, I told them I had started my degree.

So for months I've basically been pretending to be an undergraduate student.

I've been answering questions about school, acting like everything is normal, and hoping I could somehow fix the diploma situation before anyone found out.

Yeah.

That obviously didn't work.

My dad doesn't know much about university administration, but he's apparently been suspicious for a while. This week he's planning to go to the university administration himself to find out what's actually going on.

I don't even know which day he's going.

My mom was the person keeping me informed about his plans, but today I finally admitted the truth to her.

She was understandably upset and basically told me she wants nothing to do with the situation.

And honestly, I can't blame her.

So now I'm sitting here realizing that my dad could walk into the administration office any day this week and find out that his child hasn't been studying for the degree they've been claiming to study.

I feel like I've dug myself into a hole and then handed someone a shovel.

The worst part is that I know exactly what I should have done.

I should have told them last year that I hadn't completed the diploma.

Instead, I was scared they'd be disappointed in me.

Then I lied once.

Then I had to lie again to maintain the first lie.

And now I'm at the point where there's basically no way to keep the story going.

I'm seriously considering telling my dad everything before he goes to the university, but I'm terrified of the fallout.

I know I screwed up. I'm not looking for people to tell me I'm innocent.

I just genuinely need an outside perspective:

Do I tell my dad everything before he visits the administration, or do I wait and deal with it when he finds out?

I still have the outstanding exam, so this isn't a case of me completely abandoning school. I can still finish the diploma and hopefully proceed with the degree afterward.

But right now I'm absolutely terrified of having that conversation with my dad.

TL;DR: I failed to take one exam that prevented me from graduating from my diploma program. Instead of telling my parents, I lied and told them I had already started my degree. Months later, my dad is suspicious and plans to visit the university administration this week. My mom now knows the truth and wants nothing to do with it. I'm considering confessing before he finds out himself.