The html-to-xlsx doesn't support natively changing the page size yet, it is in the backlog so far.
However, you can reach this with postprocessing.
Documentation
https://jsreport.net/learn/html-to-xlsx#postprocess-using-xlsx-recipe
Demo setting page size
https://playground.jsreport.net/w/admin/C3ERuayU
Not sure what you mean with "enter the sheet on one page"...