Dropdown within a modal window on mobile

I'm currently working on a solution for adapting a modal window form on desktop to mobile. Problem is, the form within the modal window contains a dropdown. The solution I currently have is as such:

Here, the dropdown summons an off-canvas window that contains all the selectable options. It requires some scrolling since there are 12 options.

I don't necessarily think this looks bad, but I feel like there is a better way to handle this kind of issue. I want the user to be fully focused on filling the form, but I am mostly concerned that it won't be immediately clear that the dropdown features more options than the viewport might support. I am also not sure if it's user friendly to use multiple overlays at once since I don't recall ever seeing this in the 'wild'.

Thanks for your time.