I'm way behind on college applications. What are my options?

I'm a 17 year old high school senior in Minnesota.

In my junior and senior year I've been in a program called Post-Secondary Enrollment Option (PSEO), which basically means I'm a full time college student at St.Cloud State University, earning both high school and college credit. By the time I graduate I'll have earned 50 credits.

ACT composite score: 29 Current cumulative GPA from my courses at SCSU: 3.3 Current cumulative high school GPA: Unknown, but higher than 3.3. Intended Major: Mechanical Engineering

I haven't sent out any college applications yet. I know I'm super late on this, but do you know of any colleges that accept applications this late in the year?

There are many colleges that accept applications for fall enrollment in February, March, and later. This site has a comprehensive list of schools that are still accepting applications. Minnesota schools on the list include:

University of Minnesota Morris (average ACT 25, average GPA 3.62)
University of Minnesota Duluth (average ACT 24, average GPA 3.43)
University of Minnesota Crookston (average ACT 22, average GPA 3.16)
Minnesota State University Moorhead (average ACT 22, average GPA 3.32)

All of those schools are viable options for you based on your ACT scores and GPA. I'd also encourage you to go through the schools listed in the link above so you can investigate more options that fit with your location, qualifications, and major preferences.