The upbeat is usually done on the dominant chord. I find it weird that your upbeat begins on the tonic. Your rhythm needs work. We do not want just minims all the way through the passage. The use of non chordal notes or some other rhythm needs to be introduced.
Also to have a cadence that ends on the tonic in the middle of a passage is just simply not good. The tonic relieves tension and to give a sense of finality in the middle of music is just not good.
Your soprano voice is stagnant around that Bb. You should when you write the soprano voice consider the soprano voicing as the writing of a melody. You have to write this melody in accordance to your chord progression but still the melody voice needs to be interesting.
Your chord choices also seem a little off. You can very easily make the upbeat a dominant chord in first inversion which will lead much better to a tonic in root position.
Also for the last two bars you can very easily break from your Primary chord shackles by introducing the chords V - vi (2nd bar) and then ii - V (3rd bar) Which will add a great amount of new tones to a harmony that is as is very strong on the I -IV - V idea.