So, I finished all the optional scenes and got good points for all of them, but I still can't get the good ending for Alice's route. I know in the guide it said that art is the primary skill to focus on, so art is my highest skill. Is there anything else I need to do to get the good ending?

If you're asking about Golden Ending to my understanding you need to have a very high affection score with Alice, make choices in a story that won't track points leading to bad ending and play all of optional scenes

Sufficient art skill is needed to access the five different music scenes as well as a fair amount of extra affection points. 
If you're really stumped then you can jump to it in the debug menu; the script global file details the code numbers of all the scenes to navigate to them.