How to progress in the beginning-stage of screenwriting?

Hello r/Screenwriting!
Here's a little summary of what I'm about to say, so you don't have to bore yourself with my life story:

I'm trying to get into filmmaking - screenwriting is a part of that. I've never really had time to practice, and now, when I fight my way to get more time, I don't see much progress and I'm a bit lost with how to get started, get better and see progress.

I've got a bit of a 'goal' of some sorts; Write, Direct / Shoot & Edit a Short Film before I apply to the Lodz Film School in Poland next year.

However, I'm catching myself in a bit of a plateau and I have no idea how to get out of it and progress. I must admit, I'm a bit of a perfectionist - in a bad way. I've gotten stuck in this routine of cutting where new, 'uncomfortable' (?), creative decisions are... well... uncomfortable (although I'm not sure if this is clearly the issue, I do see the problem potentially being fearing failure). This editing routine is so set, I've essentially mastered it, and I don't see any errors.
All my life I've been praised for being better at everything without much effort, and now, when I'm getting into this new world... it's hard.

Any tips on how to beat this? Any exercises? Things to practice?
How can I get into a routine when I'm almost beat of ideas?
How to get over the fear of failure?

Here's the long story:

I'm a 17year old guy who hopes to one day be in the filmmaking world.
I've been a video editor for almost 6 years now, and started getting more into real 'filmmaking' this year.
Apart from video editing, I do some photography and really seasonal cinematography here and there.

As of right now, the three worlds of film that amaze me are cinematography, directing and screenwriting. It's those three I'd really like to get good at... and I can't find myself really any way to practice these.

School is ending this year, and I'm hoping to get into the Lodz Film School in their Cinematography course. I have my reasons to go to a film school.
One of the requirements is a five minute film showcasing your cinematography capabilities.

I've decided, I'd write a short film, direct the short film and shoot the short film all together.
I have a few connections in the cinema industry here in Cyprus, and I believe it's something achievable... if I can get past the writing stage.

Essentially, for the past 3 or 4 years I've gotten myself into this consistent routine of:
school - editing work - gym - sleep. I never found any time to really practice this amazing artform. Recently, I've decided to work every minute from Monday to Wednesday, in order to free up time after school on Thursday and Friday, alongside parts of the weekend to work on my craft. This is what I've done this week.

It's now Wednesday afternoon, I skipped school to work on this short film idea I've been working on... and I've practically written 3 or so pages in about 5 hours.
On top of that, I'm constantly second-guessing myself, doing way too much research behind the realism and I'm generally scared of this script not making sense, having too many mistakes or just simply not being GREAT.

It's quite demotivating, and as the day comes to an end, it only lowers my mood and motivation. I'd like to get over this, build a routine and start improving and seeing progress.
I'm not sure how to, though, and was wondering if you lot have any 'professional' advice.

Any and all criticism, 'bullying' and advice, harsh and polite is accepted and welcome. Beat me all you like, just please don't tell me "you're still young so it's okay".