Answer:
Here are the corrected sentences with the appropriate forms of the adjectives and adverbs:
1. Shayna is the best athlete on the whole team.
2. I play the piano badly.
3. Daniel plays the guitar well.
4. La Vista Grande has the best happy-hour deals in town.
5. I like goat cheese better than blue cheese.
6. I don't sing well enough to be a professional musician.