Otherwise, open up the Software Center (on the launcher), then do a search for "gm-notify". Once you've found it, mark it for installation, then go click "Install". Once that's done, you can launch it from the Applications lens by typing in "Gmail" and selecting it. Once it's launched, you can then configure it.
I live in India and I've set my update server to default ubuntu server. This is how it looks :
Try changing your update server and see if that helps. I've found that the IIT-M server (which I used for a bit) is heavily behind. However, I haven't gone back to it and have relied on the main servers since then.