Keywords in URL's are just one small factor. Google has over 200 factors in their algorithm - just use sensible SEO techniques.
If it's not an exact match don't worry about it. If it is an exact match then I think it will give them an advantage, in which case just keep building good quality backlinks to your site. As someone else pointed out above, the keyword in the URL is just one of many factors, so don't get too hung up on it.
This is very small factor, an exception: if the domain is the same as any keyword eg: keyword.com -> keyword
Don't worry. same problem here, but i think you need to do more hard work for getting quality back link. see competitor back link and used them.