Can I be convicted of a DUI?

I was with a friend and pulled into a gas station so he could use the restroom and I could buy cigarettes and he could take over driving. We parked and I drank some whiskey and a couple beers I was saving because I was the DD and we were switching drivers. There was a cop parked in front of the gas station before we even pulled up and he was inside buying food and drinks. I go inside and asked for cigarettes but didn't have my ID so I got declined and I went to grab a beverage. The cop came up to me and said he can smell alcohol on me and I told him I just drank some whiskey and a beer when we parked that I saved from earlier in the night because I was the DD and we were switching drivers when we left the gas station. He said that he saw me closing the driver’s side door and that because I have alcohol on my breath that I am suspected for driving under the influence. He wanted me to do roadside tests outside so I complied and did them just fine and he told me I failed and was being arrested for DUI and I was brought to jail. They allowed my friend to drive the car home without being tested for alcohol or anything. When I was released My ticket said Charge one: DROVE motor vehicle upon highway while under the influence of drugs, alcohol or both. The gas station they arrested me at was nowhere near a highway and I did not drive on a highway one time that night. The officer did not see me driving or operating the vehicle all he saw was me closing the driver door. I denied a breathalyzer test and did a blood test that they said would take ten weeks to get the results and they still charged me with DUI so I plead not guilty and I'm fighting the case in court.