The clerk said now I must plead not guilty and go in front of the DA, do I need an public defender for this matter?

Me and two friends from school A & B were coming from Webster Texas on our way to Galveston where i currently/temporarily reside. As we got on the freeway in Webster, I was arguing with my friend B which was in the back seat. As I was turned around partially, yelling, I veered into another lane, as we passed an officer sitting in the emergency lane. He pulled us over and continued to approach the right side of the car. As he approached he asked for the passengers licenses. As they handed the licenses he smelled marijuana(assuming he did). He had them step out and asked them to put their hands behind there back and proceeded to arrest them. Before handcuffing A & B was asked who was responsible for the weed. Well after being handcuffed A replied it was his, even though B had some on him as well. After the officer put them into his car, his partner who had came to the scene, asked me to step out and walk back to the rear of my car. He then arrested me, no questions the whole time, and then I proceeded to the Webster Jail. Okay, So I had nothing on me! What should I do? I do not have a texas drivers license, so I am not able to take the diversion offer from the court. Which was 90 day driving probation then my record would be clean. I am about to graduate with an associates of science in Mathematics on May 10, only 9 days after my court date of May 1st and I have prior intentions of attending Butler University in my home state of Indiana. I also have a clean record. Please help me solve this issue. Thanks!