Obviously I haven’t seen the letter or been given the full details of your case… but I would expect that the Job Centre is correct and the appeal will not affect your benefits.  The letter is probably a standard letter and has that note on the bottom to encourage you to reply in a timely manner. 

If you have decided to drop the appeal you should respond to the appeal letter confirming to that department that you have dropped the appeal and accepted the original decision for a 2 week sanction.

I hope this helps.