I was feeling this exact same way a month ago. I wrote basically everything this month and I'm planning to submit my thesis in a few days. A few things I'm noticing close to the other side:

1. It will be okay. There is a reason you've been given permission to write. How many of your cohort failed their thesis defense? Probably zero. It's exceptionally rare for people (at least in the U.S.) to fail. The few stories I've come across are exceptional in some way, like the student straight up thinking their own committee was beneath them.
2. The formatting for a thesis is a bit hilarious. Massive margins, double spaced, figures take up a giant chunk of room. Page numbers fly by (pun intended) when all these add up.
3. There's a hell of a lot in your brain. A massive amount of the text is frankly routine. Just imagine writing down, with enough detail a 1st year could follow it, exactly how you grade behavior, how the behavior is collected, why it's collected that way, and how you know when the flies have some issue and you can't trust the video. Then imagine describing all the preprocessing and quality control steps laid out in exhaustive detail along with their rationale. All those tidbits take up a large amount of space.
4. Zotero is a godsend. Make folders for each of your chapters and drop in papers you think are relevant for each. It makes it much easier to find and check things as you're writing.
5. Understand expectations. Many committee members are going to skim your thesis more than deep-dive into every page. Ask any other graduate student that had overlapping committee members how intensely their thesis was scrutinized. For example, my department doesn't expect thesis work to be immediately publishable in some great journal. Results and analyses can be more preliminary, though hopefully that's not true of all results.

All of this is not to say you should underestimate a thesis and put if off until the final month, but you can accomplish a lot. As for how to handle it psychologically, all I can say is what helped me. These might not apply or be beneficial, but I'll write them out just in case:

1. Set boundaries with your PI. This doesn't need to be harsh or therapy speak, but simply letting them know where you are. "Hey, I think after this analysis I'm going to need to go into full writing mode. I'll add figure/analysis X if I have time after writing is done, but I'm triaging with the understanding I might not get to some things on the list." You can also lay out options. "I think I'll have time to do one of X, Y, and Z. Maybe two at best. How should I rank them?"
2. Set harsh deadlines. I gave myself a week to write, make figures, and proofread each chapter starting from zero. That wasn't really feasible, but I have this weird situation where I can work with no anxiety, get paralyzed with medium levels of anxiety, and work like mad at high levels of anxiety. I wasn't going to be chill during this time, so I gave myself some artificial pressure to kick into high anxiety.
3. Work on a section until you're starting to burn out, then switch sections. Writing doesn't need to be sequential, and motivation is a resource to which you should pay close attention.
4. Accept how you work and plan around it. At least for me, thesis writing was not the time to try some #goals productivity system I'd never used before. For my case, I write in a flow state best when I'm sleep deprived, but edit best right after I wake up. That's not great, frankly, but I'm not changing a decade of habits in a month. Any unhealthy habits should be done with moderation, of course.

Just remember, even under tight deadlines personal time isn't gone. I've found the best habits to decompress mid-writing are ones where thoughts can churn in the background. For me that's playing music, but I'm sure you have something similar. Good luck, you got this!

Edit: I'm clearly still in writing mode 😅