Honestly wondering because I've fortunately not needed to budget this closely before: OP said $350 for food and "500$ left for things like going out, clothes, etc.". Does that not cover what you bring up? ~$11.60 per day for food seems enough for a healthy three meals a day for one person - a quick google shows numbers like $250/month on a "moderate budget" for food. I feel if you're eating one $11 meal every day that's probably a good place to start cutting down on the spending. Is $500 not enough for toiletries, dental, clothes, etc.? Looking at the past month of my own spending, I bought a couple rolls of toilet paper, a tube of toothpaste, body soap, no new clothes, some skincare stuff, and probably $150 worth of insurance. Maybe I forgot a ton of things but I don't think I spent close to $500 on the "extra necessities", as I would call them.
Just to be clear, I don't disagree with you that $21600 is too little to live on. But I mostly buy OP's numbers, which makes me wonder what I'm missing. Debt payments, maybe?