Put "direction both" in your stage text.
direction {dir}
~Determines which direction the screen scrolls in.
~{dir} can be right, left, both/rightleft, up, down, in, out, inout, outin, or leftright. Defaults to right if not declared.
up and down scroll background up and down respectively and automatically. You cannot scroll left or right in these stages. You must use groups to control enemy spawning. Wait doesn't work well here so that means you have to watch the time here. Put time item or simply set time to 0. Panels, neons and screens are not scrolled.
left and right must be scrolled manually, like normal.
both or rightleft is pretty neat. It's like direction right but it allows you to freely scroll left or right. When you reach a wait, you won't be able to move back past the previous wait until all spawned enemies prior to wait are killed.
leftright is similar direction both but it's like direction left instead.
in and out is new scrolling system in which player scrolls in or out respectively. In means up in z axis while out means down. Just like left and right, it must be scrolled manually.
inout and outin is similar to direction both but they are like direction in and out respectively.
~Screen, neon, water, etc don't work well in direction in, out, inout and outin.