Usually the way I've gotten it to work is to select all the data in the spreadsheet, copy it, then paste it into textpad or other text editor. Then copy and and paste it again into the Traveller map site. Usually I have a copy of the header information from another sector as the top part of the file where I'm pasting (first pass).
If you save as Tab Separated Values, that should just work (if you have the header row right). Usually that's what Excel puts on the clipboard if you select all cells and Copy, so you should be able to just Paste into any of the form fields that take sector data.
Much obliged. I know there was a way... slowly coming back to my mapping madness after a few years break. Appreciate it. And appreciate the map Tash, its a beaut. I procrastinate entire hours playing with it...