Wrongfully arrested for possession of cocaine?

I was arrested, booked and charged with possession of cocaine. The cops didn't field test it and umed it was cocaine because it was in a cellophane bag. Well it was a powdered doughnut wrapper i bought at a 7/11 store. Me and my friend were then arrested and booked. We posted bail at $400 each. I saw a judge the next day and was released with the case dropped. My friend was held for 5 days because he is on probation. They sent the wrapper for testing and decided there was no cocaine and didn't have a case. How would i get my $400 back? I need it for rent and bills or i am out of an apartment.