Yep.. That's why flex track is preferred over sectional track for building permanent layouts. You are not limited to the rigid curvatures of sectional track.
If you want to have something for quick-and-dirty running and be able to pack it away afterwards (like a circle around a Christmas Tree), then you want to use sectional track with the plastic roadbed, like Kato Unitrack.
Flextrack is for permanent fixture on a layout though (It won't stay at the curvature you want unless you fix it down, either with an adhesive or with nails).
BTW how big the curves are depends on what you want to run. If you want to run big locomotives like 6-axle 4th-generation diesels, you want curves bigger than 22" radius. If you want to runs big nonarticulated steam locomotives with 4 driver axles or more, even bigger radii is a good idea.
Good luck!