PLEASE HELP!! I messed up while coding!!

I made a big mistake while coding and now when I go to the pages on my site it says there is an error in some line of coding. The link is http://gadgetjunkieblog.com/?page_id=115
How do I reset the coding so it will go back to how I got it? Because I haven’t messed with the coding other than this, so I won’t be losing anything.

PLEASE HELP!!