Tile walls

I am tileing my shower in my bathroom I had to start form scratch I put up all new 1/2" drywall the green stuff and then 1/4" Hardibacker over that. When I was screwing the backer board up I noticed that there was a stud missing at 16" on the to short walls. The area to be tiled is 3, wide there are studs at both ends but only one at 16" then its 20" to the next one. I was wondering if this will be a problem when I put the tile up I don't want it to sag and crack? If it is a problem I will have to unscrew the backer board and then unscrew the drywall and install the missing studs.

Thanks
Shannon

 

I think the 16" on center rule is more critical to floors. If the wall feels pretty solid, I'd go for it.
The use of drywall and hardibacker at the same time is a little confusing. Usually the use of 1/2" Hardi or cement board nailed to the studs gives you the best waterproof subsurface.