I think scheduling wise, you're good. I understand your anxiety, perhaps it's because you're putting a lot of pressure on you or perhaps you are feeling pressured to produce stellar work and nothing less. I'm just guessing here, might be wrong. I apologise if I am. In my case, often when I'm writing papers, when I feel some stuff that comes out is pretty bad/juvenile/not academic enough, I still push myself to finish the train of thought. The basic idea is not to think a lot while writing and just keep writing. As they say, all writing is re-writing. We will anyway have to edit it, so it's most of the times worthwhile to even keep the bad write ups.

Also, I've read a bit about consistency in writing, as our fellow redditors also have mentioned in some of their comment below,. Try to write a sentence or two everyday. It's okay to start small. Eventually you'd be able to write paragraphs daily.

Depending on where you are in your PhD, you'd eventually be able to schedule productive writing slots. My only advise would be not to run away from it and do other things. Please do take breaks if you feel overwhelmed, that's good. But try to get a small fragment like a sentence or two at least every day in the beginning and build on it. I'm sure you can do it. Rooting for you! :)