>I was expecting them to be more firm inside.

GANACHE TRUFFLES..... EH?( <grin>

1)Try to replace a quarter to half of the cream quantity with sweet
butter and see for yourself the results.

2) Another thing is if you add a half of the chocolate in tempered
state but still fluid will improve the consistency.

3) Another alternative is to incorporate a small amount of cocoa butter
into the mixture.