Is there really a one true denomination?

I've heard many say that only this or only that denomination is the true one and only by following that one will you be saved.

I've also heard people say that as long as you believe in the core things like the trinity, you are saved.

Is there any truth to these statements and should I be worried?

I myself am an evangelical lutheran and i'm pretty sure that if for example there is only one true denomination that it is not mine. I still do like my denomination and I don't really have a good opportunity of joining and participating in another denomination in my country.