I think i'm going to lose my first grow (LSD-25 autoflower)

I would also stop spraying the leaves unless you see a mag deficiency. Then you spray with a little Epsom salts mixed in with your water. My entire grows, I never spray leaves

Seem pretty neglectable to me, few burn or deficiency could sometime show and don't necessarly spread afterward. so if it stay as is and don't spread i wouldn't bother too much about it.

Never use NEEM OIL !!! That's first ;) Second - most probably it's aftermath of pH already. Overwatering and wrong pH is causing such rust spots, it will go worse each day, some damage is done and you can only stop this . Results will be visible in a week only. During next two weeks on damaged leaves it will be more and more those spots even if you start to do everything right from now. Dry/wet/dry/wet or in other words good watering regime is essential. pH goes together. Those two will bring you some harvest already without any nutes in soil. 0.5 ml/l of CalMag, some veging nutrition with 50% dose would restore her back . Let her dry out each time before watering, your pots should be light. The rest was explained above. I doubt it's rusty mites man ;))))

I am no expert so take it for what it is, however, i used Neem oil and spray into soil as well as foliage. For my case of rust mold i did a small daily dose and after about 2 weeks it seemed to clear up pretty well. I hope this helps and good luck