Hi there 

Thanks for reaching out in the Lucidchart Community! It looks like one of our agents has responded to your support ticket with a solution to the issue you are experiencing – it was due to an overlapping slide at the top right of your diagram which was exceeding your page boundaries and causing the exported file to include the blank area covered by that slide.

Please note that when troubleshooting with you via support ticket our agent didn't use an extra feature – you have an Individual subscription and the presentation mode is available to this account level. If you type in "Slides" or '"Presentation" into Feature Find you should be able to bring up the Slide Deck shown in the gif. Alternatively you can access that feature by navigating to Insert>Presentation Slide in the File Menu at the top of your canvas. 

For those interested in learning more about how to export a Lucidchart document or use our presentation mode I’d recommend taking a look at our Export or print a Lucid document and Create a Presentation articles. Thanks!