It is Question 2 under Section 1 on "Connecting Root Position Tonic and Dominant Chords" from Problem Set 4 of Artusi, which my Music Theory II class uses.
The only feedback I get from Artusi is "Your progression is missing the third in m. 1", which it wouldn't expand on.
I still can't figure out how to make it 100% correct, so any guidance will be greatly appreciated!