Hi Batfan10,
Looking very good! I was glad to find your sculpt! I'm also working on two apes (gorillas) and have been collecting a lot of reference material. Like you, I started with a larger muzzle and had to sculpt it smaller... it turns out that the actual muzzles were smaller than I had imagined them to be (and just looking at the makeup with the wig it's tricky to scale it).
Like micdavis says, the jaws are not much wider than the actors lips. I also discovered an interesting thing about the jaw from the film apes... it does not extend below the bottom of the actor's chin. See these pics below, you can clearly see the actor's chin with the ape jaw sitting above it:
MOD EDIT: Link removed due to virus alert
Roddy McDowall as Cornelius from the original POTA 1968
Sal Mineo as Milo from Escape from the POTA 1971
Having said that, Galen from the TV show seems to be VERY different.
The prosthetic actually goes UNDER the chin. It's hard to tell if the jaw is actually any BIGGER or if the extension on the sides and below the jaw is just a thin layer of latex flush with the actor's lifemask... in any case it's very different from Cornelius.
Galen prosthetic
Check out the link here for more great galen prosthetic references:
Planet of the Apes - the Television Series
Anyways, just something to keep in mind, as I noted that your ape jaw seems to go quite a ways below the actor's chin (as below), you may want to consider sliding the jaw up some so the bottom of the ape's jaw & actor's chin are more aligned... the downside is, of course, moving it may require some changes in the upper muzzle to sync up with it...
I hope that helps! Looking forward to see more!