Just bought the fake pass from the guy outside of novigrad, but when I talk to the guard all i can do is ask him where to get passes?? WHy cant i get in?

You can't get in because you bought it from a "Shady" guy. They are fake.

You can get a real one from a contract for the Shrieker (can be mistaken) from the chief of the guard or whatever he is called, can't remember the name.
And I've read somewhere that you can get one from the Baron but not sure, I got mine through the contract.

If it makes you feel better, I made that mistake, too. I even did the quest to get the discount, but accidentally got the guy's brother killed (oops), so no discount for me. Of course, now I feel cheated (and rightfully so; I done goofed).

You also get one from the bloody baron if you follow the main story for a while. Since after a certain point you need to get in to the city and he gives you a pass

Exact same thing happened to me. The game bugged out a bit though and the quest just vanished but then reappeared later under "Failed Quests". I did get ripped off by the guy though, but that's part of the elegance of the game I guess. Tough choices with no obvious right or wrong, no obvious win or lose and an occasional element of "life sucks, tough luck" just like in real life. I suppose that's cool in its own way though too. :)

I haven't tried to buy fake paper, but captain of guard indeed gives you pass (as well as Red Baron, but under different circumstances) if you complete his "monster hunt" quest. It's no Shrieker, Shrieker is near Crow's Perch.

I spoke to the guard before buying the papers, and asked him where to get them. He said something along the line of 'you don't'. I bought the papers and went back to him. He paused, and I thought 'oh, shit', but then he said 'doesn't look dodgy' (or words to that effect), and I got in. They are not useless.

I got the real paper from a quest, but then went back and did the Fake Papers quest for the exp point. :D

Yeah i got mine from the Baron and it was legit though he has forgot to put the stamp on it xD

I used fake papers successfully. When the guard mentioned it was missing a seal, there was a dialog option to convince him whoever wrote it was in a hurry or something and he believed it! I don't think it was even an Axii mind trick. :P

I got the papers, then sneaked into Novigrad through the harbor. So no completion of that part for me.