Saving and Exporting files

Thank you for helping a novice.

I have a 3+ hour video, about 520MB. I cut out a 50 minute segment from it and save it as another file. Then I export it. I have tried 3 different settings, but for some reason this small 50 minute portion of the 3 hour video exports bigger than the original video! I am lost. the 50 minute video was at least 750MB when it exported. Sometimes too when I export it just decides to crash. But the size is really more of the issue.

What am I doing wrong? Thank you for your help!