If I do that it doesn't get any bigger just makes the window bigger, not the image
If that is the case something is wrong with your set up. The slider bottom right Yammer p pointed you to does alter the size of the thumbnails, not the panel itself.
Top right are the workspace names, at the right of it is triangle, click on it and choose reset workspace. Otherwise restart bridge holding down option (mac) or control (win) when restarting bridge and choose reset preferences.
If still out of luck provide more details about your computer (RAM / VRAM) OS version and exact Bridge version.