I select the rectangle tool and drag a rectangle to the size I want and when I fill it, it fills as an oval or circle. I did not choose a circle. What am I doing wrong?

Okay, figured this out myself. I was opening a file previously created and, in that file, I must have dragged a corner handle on a rectangle along the side which created curved corners or something like that. Apparently, when you do that, it stays with the rectangle tool each time you use it in that particular file. Closing Inkscape and reopening (starting a new file) this problem does not exist.

Live and learn.

For future reference, when in the rectangle tool the last button on the tool control bar will set the corners back to 90°.

Thanks Xav, good to know.