1366 x 768? Are you trying to run Animate on a netbook?
The export window for animated GIFs can be resized, but it has an absolute minimum size of 950 x 800. So unless you can increase your desktop resolution, you're out of luck.
Im using win 10 on recommended resolusion wich is 1366x768
Later versions of Animate fixed some issues. If you're not on the latest version try updating. If you are on the latest version you should report a new bug: Feature Request/Bug Report Form
The work-around for these problems in older versions of Animate is to go to your desktop and right-click select Display Settings. In there is a scale slider, that makes applications appear bigger than normal. Try moving that to the default setting, which is often 100%, but sometimes 150 or 200.