All the ているんだ can shorten into てんだ?
 

I wonder If all the ているんだ can shorten into てんだ?


For example, やっているんだ ----> やってんだ

書いているんだ　---->　書いてんだ

寝ているんだ　---->　寝てんだ

Is there any exception that can't be shorten into てんだ?

I'll stick my neck out and say that I don't think there are any exceptions. :eek:

True but the more important truth is that native speakers don't use だ as a neutral sentence-ender that the OP appears to have been taught to use.

I (a native speaker) would have to be fairly irritated or unusually determined to write something to ever say　書いているんだ or 書いてんだ. At least the OP should know that he will look more than goofy if he finishes every single sentence (or even one out of every 4) with だ.

What ending should I use if I want to sound natural?

It depends on whom you are talking to.

What if I want to use male speech to my friends?

Like i want to say "I will go to movie tomorrow"

明日映画に行く<--- Does it sounds too feminine?

Edit: Whoops, I misread your post. I'm sorry. :/
I agree with MMM's comment below.

That doesn't sound feminine at all.