Thanks for your question.
There is no requirement for the folio to have both formal and creative writing, so my advice would be to submit your strongest pieces. If they are both formal, then that’s fine.
I could try to give you some quick tips about what makes a good piece of creative writing, but really it’s most important that you look at what the standard is asking you to do. If you can craft a piece, which is controlled, and develops and structures ideas and uses language features that are appropriate to the audience and the purpose of the piece, then that is the most important thing. Check with your teacher if you’re not sure what any of those things are, and maybe ask how they would play out differently in creative and formal writing. Read some short stories and think about how ideas are developed in them. Perhaps the language features may be more poetic. There may be more deliberate ambiguity, more attention to rhythm and sound, more creative use of long and short sentences. A creative writer may make the reader work a little harder, saying less and showing more.
Another thing is the importance of editing, whether the piece is formal or creative. That’s the ‘crafting’ part of the standard. Make sure every word is there for a reason. Ask yourself what purpose each word serves and if you can’t see what it adds to the piece, get rid of it.
All that aside, as I said above, you can absolutely submit two formal pieces if you think they are your strongest ones.