How do I get back a section I deleted without having to redo the whole thing?

I accidentally deleted a whole section. 

I can see it in the drop down menu of "revision history". Unfortunately its not the last thing I edited. When I click on it, it reappears like it was but won't stay once I exit the drop down menu. 

Is there a way to fix it without redoing the whole section ?

You can use the Revision History then click Revert in order to bring back to that revision. However, note that since it is not the last action that you have done, it will not just bring back that certain field, it will completely revert to whatever is in your form on that certain revision.

https://www.jotform.com/help/294-How-to-View-Form-Revision-History

If you don't want that route, unfortunately, you would have to manually add the whole section.