A poor result is usually fixable. The model can do good work — it just needs clearer direction and a little iteration.
Tighten your prompt and lyrics
Replace 'make a song' with something specific: genre, mood, tempo, language and vocal type. Then check your lyrics — overly long lines or odd phrasing make the vocal sound forced.
Iterate, do not restart
Generate a few variations and keep the best. If only one section is weak, use section editing in Autunes to regenerate that part alone, and use stem separation to inspect whether it is the vocal or the instrumental causing the problem.
- Variations to find a better take.
- Section edit to fix one part.
- Stems to isolate the issue.