Any tips for beginners? My remix is all over the place.

I want to create remix versions of my favorite anime BGMs. I'm a big fan of youtubers who remix battle themes anime bgms with heavy metal and intense drums. I recently discovered SunoAI and tried the free version first.

However, I noticed that I can only upload music that's 1 minute long. I don’t understand why it's limited to just 1 minute and not the full song? If I get the premium subscription, will I be able to remix a full 4-minute track?

Also, I’m not very experienced with music AI prompts, Ive tried the free version, I uploaded an anime bgm music, then add my prompts like "battle theme, metal, heavy metal guitar, heavy drum" something like that. The results are kind of... not sure how to explain, its like the music is all over the place? So Im probably doing it wrong right?

I've only used NovelAI for images before so I have no experience in music prompts. I’d really appreciate any tips or advice before I subscribe to the premium plan.

Thank you.