...you don't really go back to the starting line.
You don't go back to where you started.
You don't go back to the beginning and start all over again.
Isn't that a relief?
Now, you just have to pick yourself up, dust yourself off, gather yourself, and press on once again.
Stop worrying about your latest slip up and your latest stumble. You didn't go back a single step anyway, unless you chose to do so. Going back is really up to you.
You need to start only where you stumbled. You can only go forward from there.
You are still close to the finish line. Press on!