I just calculated my final GPA for sophomore year, and it’s a 3.65. My GPA from freshman year is a 3.81, so overall that averages out to a 3.73. Should I be concerned, especially considering that my grades decreased from freshman to sophomore year? My dream schools are prestigious but not crazy prestigious liberal arts colleges like Vassar and Wesleyan. Are they kind of out of the question now?
Well, first of all you calculated it incorrectly.
You have to take all your grades divide it by all the courses you taken
So for example if you had 8 courses, then so far you would’ve taken 16 courses altogether.
Add up grades of all 16 courses and divided by 64…and when you add up the courses, note if you are doing weighted or unweighted
I don’t think that would really work because some of my courses are full-year while others are only for a semester, so they receive different amounts of weight without being “weighted” in the AP/honor sense. I kind of doubt the number would come out very differently if I was able to do it that way though. But anyway, that wasn’t really what my question was about. I think people will be able to tell what my grades are like from the numbers I left. Sorry if you’re confused by them.
Nothing you can do about it now. Just work your butt off junior year to get all A’s.
You want to show an upward trend, so as long as you increase you gpa higher than both your freshman and sophomore gpas, it should be that bad.
All you can do now is work hard and see what happens next year. Also study for SAT/ACT. If those schools don’t work out there are many other great LACs that are slightly less selective. Soph.year is way to early to decide on “dream schools”.
Your cumulative GPA might not actually be the average of both of your GPA’s. I made the same mistake, and had to go through the pain of having to recalculate the whole thing. 
As someone else said, there’s no point in worrying about it now. Your GPA isn’t bad, so don’t stress it. Also, although GPA is a big factor in college admissions, it’s not the only one. If you took more honors and APs this year, or did more extracurriculars, admissions will be happy to see that you pushed yourself.
Junior year is hard. Nothing panic-worthy though. Just watch your workload, and study throughout the year for your ACT’s and finals and what not. Colleges will love to see that you made a comeback. 
Best of luck!
Check the Common Data Set (Section C) for Vassar and Wesleyan to compare your stats to those of admitted students. If you are below average for their admitted students, you will need something to make yourself more attractive that off-sets that - realizing that GPA is a very large component of the ‘first cut’ in admissions decision-making.