Thank you so much!!
Ahh I don't want you to be stuck. There are several options and ingredient values are reset inbetween the scenes, so if there really is a problem in the code, I am sorry. ðŸ˜
Talk to the witch and she will mention she should have known that the cauldron is already heated up (+50) through the fire. That means you need to add 340+ to reach the 390°C goal.
Try the necklace (+40) instead of the (+60) item. It's in the drawer on the right side of the room. If you have used it up for the first round, try the plant (+40) next to the drawer instead. It should make you end up at 340°C with the crystal (+200), fairy(-100) and either mouse or gnome (either +200).
Adding 50°C from the heated up cauldron it's exactly 390°C.
If this is still not working then I'm so sorry 🙈 You might have to try to reset and if I made a mistake (either wrote 360°C somewhere or an item doesn't work) I need to fix this after the voting period.
I am still thankful you enjoy the art and everything!