Mountain Lion is OS X version 10.8, so no, you do not have Mountain Lion. You have Lion.
You will not lose all the programs or all the documents. But it is possible that some third party software does not run under Mountain Lion. Here's an article about it: http://support.apple.com/kb/HT3258
The one program I know that ran under Lion but is not quite ready for Mountain Lion (though the developers are working on it) is TechTool Pro 6.
Also, not all MacBook Airs are compatible. Your MacBook Air must be from late 2008 or newer to accept Mountain Lion.
I have a mid-2012 MacBook Air, and Mountain Lion is great for me!
Good luck. I hope you use and enjoy it.