hybrid bike ... too small? risks? I bought a Schwinn from a big box.  I'm regretting it for technical reasons (shifters, brakes), but I'm starting to wonder if the frame is too small.  I have the seat way up and going down steep (paved) hills is a bit scary.  It feels a bit unstable.  It's a hybrid because my wife and I like to go on the C&amp;O canal every now and then, but I am starting to put the miles on the road when riding alone (see the aforementioned hill... we have LOTS).  At 6'1", with a 33" inseam, should I have concerns about this 17.5" frame?
There is danger and there is discomfort...you should accommodate both. 
There is a max insertion line on the seat post - do not ride the bike with the seat post extended beyond that line, buy a longer seatpost. Though I would imagine that a standard 17.5 frame would accommodate a 33 in inseam (is that your real inseam...or the length of trousers you prefer? There is a difference).
If the reach to the bars is too short, bringing your hands too close to the hips for your center of gravity, then you will feel that you don't have a lot of steering control.
It sounds like the bike is too small for your comfort - some people like small, whippy bikes and others like to ride much larger, more stable, bicycles. People are usually more comfortable on a larger bike, where they can change position during a longer ride and as the terrain changes.
Good luck, and have fun riding!