Issues with sharing Power Point Presentation using second monitor

I am trying to screen share a power point on a second monitor so I can then use my main monitor to copy and paste notes in chat etc but it doesn't seem to work properly.  When I choose the second screen and then screen share portion of screen (which I have enlarged to whole screen) it's like it is mirroring the main display as when I swipe up on mouse pad the shared screen also changes.  It's hard to explain...  I have a MacBook and my second screen is a Samsung.  I need to use the second screen as when I try to share from my laptop display it doesn't seem to be big enough and appears fuzzy for viewers.  Any ideas would be appreciated...