honestly just don't be afraid to fuck shit up, like it's your fic and you can go as crazy with it as you want. you can do anything you want in your fic, the world is your oyster and reality is whatever you want it to be haha so don't think about it too much (coming from the world's biggest overthinker...no one said i wasn't a hypocrite) and just write. ultimately it's really about what makes you happy rather than crafting the 'perfect' fic because perfection is fake anyway
in terms of more constructive advice, i would personally recommend editing as you write rather than waiting until the end to edit. it helps you spot mistakes along the way that you might miss if you do one whole edit at the end. e.g. if you see a typo just correct it immediately rather than waiting until you've finished writing the fic because you might forget about it. and then do one more final edit of the whole fic after you're done writing just to catch any mistakes/change anything you wanna change. but that's just what works best for me, everyone has a different editing/writing style and it's really up to what works best for you!