You did the right thing resfusing. However, as an under 21 guy you are going to get hit pretty hard.
First, your state probably has a provision by which they can administratively revoke or suspend your license for refusing the test. For an underager, they probably wll revoke it until you are 21.
Bear in mind that this is a separate event from your criminal prosecution. The state gets away with this because "driving is a privilege".
Now, as to the DUI criminal stuff:
the first thing a lawyer will challenge is the grounds for the stop. That is going nowhere - the roadbocks have been ruled constitutional even though they are straight up Nazi Germany Jew Hunts.
The next thing that will be challenged is grounds for arrest. Did you take any field sobriety tests? Were you placed under arrest?
If you did not take the field tests or the breathalizer, then the officer arrested you based on the smell of allcohol. It is almost impossible for you to be convicted of DUI UNLESS your state has a different protocol for underagers.
Many states have a law where underagers will get DUI if they are even .02....
Some other states have laws where you can be arrested for "suspicion of DUI" as well.
In all likelihood you'll lose your liocesne until you are 21, but be spared a DUI conviction.
Talk to your lawyer.
And welcome to the club.
