Did you get a Life Tree Trinket instead of the Garnet Trinket after completing the craft 'Garnet Trinket'?
This is because the 'Garnet Trinket' craft has a chance to craft the Garnet Trinket. You will either get the Garnet Trinket or the Life Tree Trinket. If you get a Life Tree Trinket, you will need to go find another Garnet and do the 'Garnet Trinket' craft again until you get one.
In the Goal 'With Our Powers Combined...!' you will see the hint that mentions it may take a few tries to craft the Garnet Trinket. Good luck!