HTML code all messed up and now my site isn’t working!

I really need help. A few minutes ago I posted my code on this support forum (in troubleshooting section) in hopes that someone might be able to take a look at it and tell me whats wrong with it. Then I realized that is a little overwhelming for most people. I tried to paste adsense into the main index of my html code in theme editor and now my site doesn’t work at all. Does anyone know if there is any way to go back to the original version of the code before I started messing around with it? when I try to bring up my site an error message reads:

Parse error: syntax error, unexpected ‘<‘ in /home/onezerid/public_html/wp-content/themes/tigopedia-reloaded-10/index.php on line 28

Does anyone know how to fix this? I am very new to all of this and have no idea what I am doing! please help..