iPhoto Library Manager

Today, I was using iPhoto Library Manager to access different libraries in iPhoto as usual. I prefer the iPhoto Libraries system rather than Photos Libraries. Today, I made an accidental inadvertent move with the mouse. It resulted in my iPhoto screen becoming so big that I can’t operate anything from that full size screen in i-Photo. It occupies the entire computer screen. I can no longer move from that screen to a different library, or do anything else. For some reason when I open a Library in iPhoto Library Manager, I get a screen that covers the whole computer screen. I cannot make it smaller in order to work normally. This also stops me from going to other Libraries that I wish to work with. I seem to have done something with my mouse to cause this problem. Is there anyone familiar with iPhoto Library Manager that can help me rectify the accidental move I made? I have been using iPhoto Library Manager for about 15 years & love it; but now I have made a move that I haven’t been able to fix.