First time PCB design - board dimensions question
Ultiboard appears to be exporting extra fiducials (those circular marks at the top left, bottom left and bottom right of the image you posted) which are being interpreted by OSH Park, and other online PCB fab house previews, as part of your design.

For example, I use Eagle and also use OSH Park (which is what you appear to be using) and when OSH Park previews my designs, the images are essentially zoomed in on my board outline.  The preview picture will contain everything present in the gerbers... and since my board outline is the biggest thing, that's what is present in the preview.

You need to figure out how to configure Ultiboard to not export those fiducials into the final gerbers.

EDIT: I found the user manual for Ultiboard and it appears you can disable the automatic addition of fiducials on gerber export.  Read the manual here and go down to page 1-19 to see instructions for how to get to the setting.