Do i have any options?

So i was sitting in my friends car in the park parking lot at night, and a car rolls up with his headlights facing our car. I get out of the car my friend follows and then notice that this is a under cover cop getting out of the car . At this time i had a digital scale and rolling papers in my pocket and there were about 1.5 grams in the glove compartment. He asks us what we were doing and i tell him we were smoking black and milds and listening to the radio. There was a pack of blacks on the floor and he had no reason to think we were smoking pot because we had not for a few hours and did not smell like it.
He asks for our drivers licenses and then asks where the weed is. I tell him we don't have any but he just kept asking. Eventually he starts to threaten my friend by saying that he's going to impound the car if we don't tell him. My friend gives into the officer and tells him that its in the glove compartment. He finds it then searches my pockets and takes my paper and the scale. We both get arrested and charged with possession and paraphernalia. What can i do or is there not much for me.

Could i plead not guilty and say it wasn't my weed and i had no idea it was there even though i had scale and papers on me?

Did they have probable cause because we were in the park after dark?

Does it matter that this is my first conviction ever?

Does anyone know how bad these fines are? i live in New Jersey