Boss: How long till it's done?
Me: 1 week

... 1 week later
Boss: How long till it's done?
Me: 1 week

... 1 week later

Boss: How long till it's done?
Me: 1 week

... 10 months later

Boss: It's almost Christmas
Me: 1 week

This always happens the first times.
Only experience helps you not to underestimate time.
I remember a coworker had to migrate a website from Webforms to MVC. In a week he and a couple more had migrated almost everthing. Only the search results were missing:
"Monday afternoon it should be finished" (it was Friday that day)
Two weeks later we finished it.
It was hell.

@OneOfSimpleMind Wow, thank you for your comment. It is also my first time working on something this big. When I started I felt I could see the entire steps from start to end, but I was very wrong. Every feature tends to be more involved then what I expected, allot to consider and everything a rabbit whole worthy of exploration. It is a humbling and shameful experience to continuously realise you where so wrong and that you know very little.

Don't give up! I remember spending 5 months trying to get a cloud to on-prem vpn setup with no success using every method I could find. It was really stressing me out.

Then one of my colleagues told me the other side allowed him to connect with a vpn client and my problem was solved in 3 days.

@masterzen and with the rabbit hole, I spent the whole of today building my first bitbucket pipeline. There are more build attempts than lines of code and its still not working. First fighting with bitbucket, then aws cli commands and now simple bash. But I'm close! I've been close for 6 hours though. :(

@cmarshall10450 thank you. I always feel that I'm close, it's sort of a perpetual boost that keeps you going lol

@masterzen I kept working late tonight for two hours because I was just "10 minutes away". I've left now but I can't help but feel I was still just 10 minutes away and I wouldn't be thinking about it over the weekend.

My formula for time estimation is usually double the time I assume it will take, with an extra week tacked on just in case.

Multiplying by Pi seems to be a good estimate for me. That leaves time for the inevitable rewrite, plus the usual optimizing and polishing.

But it's true that the more experienced you are, the longer you'll say something will take. And the more accurate you'll be.

But remember, no matter how much experience you have, you're still guessing how long a complicated logic problem of at least somewhat-unknown scope will take to solve. You are going to be off, just make sure it's in the direction that benefits you.

I great his might get agitated and fire you

I would like to work for your boss/company.