I just realized that there is indeed a way to do what you want using native Forms 2.0 designer features.
The option is there on the field editor. Do exactly what you did for the Events option and play with different values on the "field width" and it will look exactly how you want it.
Like this:
I also realized that Marketo is forcing us to put a checkbox label option and I don't see how to not have the "Yes" next to the checkbox without using custom code. So you might just have to leave it.
We can submit an "idea" and see if Marketo includes the ability to make the checkbox label optional.
Let me know how it goes.
Good luck!
Rafael