How could I say .  you do not need to apologise or your apologising is not necessary ?

My try

özür dilemeye  ihtiyaçın yok

özür dilemeye gerek yok

özür dilemen gerek değil

Many Thanks  

Özür dilemene gerek yok.

you can say all of these, although "özür dilemene gerek yok" is the most common form

You can´t use "özür dilemen gerek değil" because it is not a correct sentence.

how come 

do you mean it needs to be "gerekli" or do you totally find it wrong 

Oh, forgive me. I should have explained it. Yes, it needs to be "gerekli". But, however, "özür dilemen gerekli değil" does not sound familiar.

thanks.

What about gereksiz ?

"gereksiz" sounds familiar when it is used in Past Tense Form:

özür dilemen gereksizdi, bence: There was no need you to apologize, in my opinion.

but, özür dilemen gereksiz....mmmm...i´m not sure. as "özür dilemene gerek yok" is used commonly, other structures sound unuseful and weird. because when it isnt necessary, we commonly use "gerek yok" for "gerek" structure.

we generally use "gereksiz" to mean "pointless, inappropriate, nonsense."

Çok gereksiz bir toplantıydı: it was a pointless meeting.

Çok gereksiz bir çıkıştı: it was a pointless/nonsense/inappropriate reaction.

thanks.