Why aren't the corners and edges of my trackpad working?

Hi

I have a late 2011/early2012 MBP running OSX 10.7.3 (build 11D50d) and All of a sudden my trackpad is playing up. I can move the cursor from all places of the trackpad apart from the bottom corners - but I can only click in the center of the pad. However I can touch click in most places (apart from bottom corners). Does anybody know how to fix this?

I've only had my MacBook Pro for 4 weeks now, I've not dropped it, knocked it or spilt anything on it, so this is pretty disappointing to say the least. I've seen a bunch of videos on youtube where people are taking their MBP apart and tightening a screw to fix the problem. My warranty is still valid and I have AppleCare so I don't want to be voiding either of those by taking it a apart and messing about inside.