I'm trying to find the verse(s) in Qur'an where it says something like "Jannah will not be according to you".
The clearest statement saying so is actually as @Abu haneef Musa has pointed out in verse (4:123):
Paradise is not [obtained] by your wishful thinking nor by that of the People of the Scripture. Whoever does a wrong will be recompensed for it, and he will not find besides Allah a protector or a helper.
Note that even there (in the Arabic text) "Paradise" or "Jannah" is not clearly mentioned, it can only be concluded from the context. As after quoting hell and its punishment Allah one verse earlier promised paradise those who believe and do righteous deeds and in this verse he just make clear that it is not for us to say or whish or declare who may enter paradise, but to Allah's just verdict.
This verse is also an answer to those who spoke the untruth about Allah and/or considered themselves as chosen ones who would never been punished or rejected a punishment in the hereafter and said:
And they say, "None will enter Paradise except one who is a Jew or a Christian." That is [merely] their wishful thinking, Say, "Produce your proof, if you should be truthful." (2:111)
And they say, "Never will the Fire touch us, except for a few days." Say, "Have you taken a covenant with Allah ? For Allah will never break His covenant. Or do you say about Allah that which you do not know?" (2:80)
But the Jews and the Christians say, "We are the children of Allah and His beloved." Say, "Then why does He punish you for your sins?" Rather, you are human beings from among those He has created. He forgives whom He wills, and He punishes whom He wills. And to Allah belongs the dominion of the heavens and the earth and whatever is between them, and to Him is the [final] destination. (5:18)
And they say, "There is none but our worldly life, and we will not be resurrected." (6:29)
And they said, "We are more [than the believers] in wealth and children, and we are not to be punished." (34:35)