Hello @holly9!
No worries - it’s just a case of Discobot being picky about the commands. The command must be written exactly as shown in the instructions, otherwise Discobot can get confused.
I wrote a bit more information in reply to your question here.
I’ll also re-write the correct dice code for this activity (the muse message) below. Feel free to give it another try! 
@discobot roll 1d9