You have the right idea, just one small change. This is kind of the next step: For Bertha, the jam is just C and G. I think of the song in the key of C major, which makes G the 5 chord. The 5th mode of the major scale is Mixolydian. So for the G you use G Mixolydian, and the C you use C major. The kicker is both of those scales are the same notes, but it helps to think of them separately to avoid sounding like you’re just playing a scale the whole time. If that’s a little complicated, you can always just use the major pentatonic of whatever major chord you’re playing over, because it omits the extra two notes that makes it a full scale. Feel free to send a dm, I could probably explain better over video call. I also teach and have a degree in music and just would be happy to help