This may be a long shot, but did you use the 'save for web' dialog?
Maybe you accidentally changed the image size yourself or there's an old value stuck in a saved profile as a preset.
Does the problem occur with every image/ image-type or just with .jpegs?
Looked around a bit on google and apparently 'it is not a bug, it is a feature'. PSE7 automatically resizes in certain situations, like when an image is dropped on a canvas in the workspace smaller than the picture (Well, PSE6 does and PSE9 doesn't anymore, a bit uncertain) or when called over some programs email function, among others not specified here at the 'Missing Manual' at google books
. But I don't think one of those applies.
It should work like this without resizing:
1.After finishing your retouching, File->Save for Web
2.Change preset in the top right corner to JPG/JPEG and check 'progressive'
3.Make sure the box below for resizing shows 100% percentage(?)
I hope this solves your problem.