If you double the recipe

Do you know basic geometry? Multiplication?

No. Not even close. Even a 9x9 would be way too big.

Only if you double the recipe.

No.

Just calculate the area and use the pan (of any shape) that is closest to that area. Also, this is what neighbors are for!

Do you have a round 8” pan, like a cake pan? I would use that, if possible. 9x13 will make it much thinner, which might change the texture and taste. As the PP said, I would double the recipe if forced to use a 9x13” pan.

You might be able to pull it off by making an aluminum foil barrier to make the pan 9x8. Alternatively, you could double the recipe and use the entire 9x13 pan. Just keep a close eye on baking time.

I want to make this recipe but don’t have an 8x8 pan. Can I use a 9x13?

https://www.kingarthurbaking.com/recipes/fast-frosted-gingerbread-cookie-bars-recipe