Muffed punt into the endzone

[rookieref2005]

In another junior high game today (NFHS), R1 muffs a punt at his 6 and it goes into the end zone where K recovers. Our line judge, a high school kid, signaled Touchdown.

After confering with him that it was a muff that travelled into the end zone with no new force, I ruled it a touchBACK. R's ball on the 20. In the book, I checked through Rule 6 and Rule 8 but couldn't find it.

My thinking was that the kick hadn't ended since it hadn't been possessed by R so the automatic touchback was sticll in effect.

Any help out there would be greatly appreciated.
RookieRef2005