It's an eighth note followed by a triplet. There are a number of different ways of playing the triplet, of which no two sound quite alike. Using two different buttons as you're doing is certainly an option, and practice will make it sound less disjointed.
Another approach is to roll the A using the first two buttons on your right hand C row--on the pull, d and (upper-case) b (when I type the character in question I get an idiotic smiley). Play the A on the left hand C row, play it again, then tap those two right hand buttons, then play the A again. The rhythm is dum-dum-ditditdit--or, with a very slight lag on that right hand tap between d and B, dum-dum-dittlydit. Either is OK. The trick is to play the d and B with so quick and light a touch that the ear can barely make out the actual notes being played, if at all. It's a rhythmic, percussive ornament rather than a melodic one.
If you're playing a 30-button instrument (I can't remember whether you've got hold of one yet), you might consider learning the tune in D from the outset. Not only will other musicians want to play it in that key; the fingerings and ornaments you use will also be quite different. That said, techniques like the roll described above can be learned on a 20-button and carried over when you make the switch; they just won't be applied in precisely the same way in a given tune.
Edited by Bob Michel, 27 October 2015 - 06:03 AM.