Zathura always displays odd pages on the right and even pages on the left. Which is how books are conventionally displayed, ie page 1 is typically recto. I don’t think this behaviour can be configured, but if you need pages 2 and 3 displayed together then your book would display correctly in Zathura dual page mode. But if you needed 1 and 2 displayed together I don’t think Zathura can do that unfortunately