I had a few minutes to write an alternate bass part that might give you some ideas.
One thing I'd point out is notice in measure 8 that I played the C note twice. The reason is that bass is usually played 1-V-1-V
Well, The V note of the Iv chord (C) is a G note. If I play the second note of that measure as a G it gives a strange sound like the bass switched chords a half measure early. If you listen hard to recordings you will findd many pro Bass players will simply repeat the root note of the IV chord before going to the I.
The same rule holds true on the last measure of the I chord (G in this case) when going to the V chord (D).
another way to fix this problem is to create a run that leads form one chord to the next (which I did going to the D in this case.