Consenual sex with a minor?

Hi, im 18 years old and about a week ago i had sex with a girl under the age of 18, after she left my house she was arrested for being drunk in public... in the police report she tells the police she had sex with me. today i got called into a detectives office being accused of sex with a minor. i denied it, he said he was sending her clothes to get dna samples. i have 3 questions. how much trouble can i get in? (the minor stated it was consensual) he asked me if i was willing to do a drug test... should i say no? and what are the chances her clothes have my dna on them if i wore a condom and barely even touched her clothes.. thankyou so much and im sorry i did this but i dont believe i should go to jail. she definetly came onto me. please help im so scared i dont want to go to jail