How do you get the Play in Browser to work with Unity. I exported the build as a WebGL and uploaded it and put HTML. It was there but it was really small and couldn't see all of the game window, so I switched it to download. Does anyone have ideas why it was small?

Then check the same for Itch.io. In Embed option you should have Embed in page and Manually set size options selected. Then you can enter the same numbers (or slightly bigger numbers) for the width and height fields than what you have in Unity settings.
Let me know if this helps.