When playing the Rhumba bass line in the key of G, you should have no problem with the G and C chords, but when you get to the D chord the fingering may require some extra practice. The real problem here is the grace note.
The D note is played with the 5th finger, then the grace note F is played with the 4th finger before playing the F# with the 3rd finger. The final note A is played with the thumb. Practice the whole thing slowly at first.
In the 12 Bar Blues ahead you will use a new technique in the right hand part. This involves playing a repeated root note with the 5th finger while moving between other notes with the other fingers of the right hand. This technique is very common in Blues. Here is an exercise to help you gain control of it.
If you’ve come this far, you should be starting to make some mighty good Blues sounds. If you wish to pursue playing Blues further, the book Progressive Blues Keyboard Method takes up where this book leaves off, introducing you to new styles such as Gospel and Boogie Woogie, as well as new sounds, rhythms and keys.
Have fun and good luck.