When I got my first DUI, I went straight to jail after being pulled over. I was held over night and let go with a sentencing hearing date. I pleaded "no contest", as I was guilty. I got a lesser sentence.
The only time I know of for someone to get sentenced more days for a DUI was when they plead not guilty. That's how my attorney told me it worked, so I did what he said and within a few minutes, the sentencing was done.
I get the scary part and I hope from everyone's experience posted here, you're left with a little less stress.