You can do that by default. Click the Advanced Setup Button in the top right corner when setting up a game, and change things to your liking.

I did that but it only lets me play on the smallest map if i remove the players so there's just 2

You can remove players from any map size by selecting the map size first and then clicking the Delete button (or whatever it's called) near the Civ Frame.

I did that. It automatically starts me on the smallest map.

That's pretty much impossible.

How do you know it starts you on the smallest map? If you've concluded that from the size of the minimap: The map grows as you explore, it does not show the scope of the map until you've reached both of its edges.

Ryika is right. You just need to try it one more time.
To show map size from the start choose a Continental Spacecraft - To show coastal lines.