You've got to get obsessed and stay obsessed

Hello! I don't know if people still have discussions on here, but I can't find any other platform where I can follow the conversation, sooo... Any advice gratefully received.♥  

I've signed up for the H/D Bang, and having finally got started with it, I'm now having a crisis that the fic I've planned is not going to reach 50k. 

The length my fics turn out is always a surprise to me. This year's erised ended up being 65k, and I had NO IDEA that was going to happen. I still don't really know how it did. Foolishly, I let this give me confidence to sign up for the Bang. After all, if I could write a 65k fic by mistake, how hard could it be to write 50k on purpose? /o\

So, I got a rough plan together and it's around 30 scenes long. No problem, I thought. My 65k erised only had 25 scenes! This was going to be easy!

Then I wrote the first scene and it's only 800 words long. FUUUUCK. What's gone wrong? No way is this going to be 50k! I looked back at some other fics. My next longest fic has 42 scenes. But it's only 41k! OMG! 

I looked at my other mid length fics.

28k = 18 scenes
28k = 19 scenes
22k = 14 scenes
32k = 19 scenes
28k = 16 scenes
34k = 18 scenes

This is reassuring. But what about the rogue '42 scene / 41 k' fic? How can I be sure this one isn't going to go fucked up like that one? 

I have so many questions. How do you estimate the length of a fic? Are you anywhere near being right when you do so? I've never even TRIED before, so I have no freaking idea.

Thank you if you can help! ♥ And I hope you are all well?