I need to remove a URL from Health -> Fetch as Google in Google Webmaster Tools.
Is it possible?
You can't remove an url from the list. Like paulmorriss said, there is no harm in simply trying again if you made a typo error in the URL. You get your 500 fetches reset once a week.
You can use this tool to fetch up to 500 URLs a week per Webmaster Tools account https://support.google.com/webmasters/bin/answer.py?hl=en&answer=158587
If you want to remove an url from the index then when you are in Webmaster Tools go to Optimization > Remove URLs and follow the instructions.