When someone has you fill out a W-9, that means they intend to send you a 1099-Misc form showing how much they paid you for your performance(s). They will also file this information with the IRS, so YES - you need to report it as income on Schedule C.
Free-lance performing musicians are considered to be independent contractors, so the amount you were paid will be in Box 7 - Non-Employee Compensation of the 1099 form.
If you were paid more than $600 for the year, the payer should send your 1099 to you by February 15 of the year following the performances (although it is not uncommon for these to be late).
If you were paid less than $600, they are not required to issue a 1099, but they may still report the information to the IRS.
If you had any other musicians performing with you, they are also independent contractors, and you can deduct the amount you paid them. If you paid any of them more than $600, then you should also issue them a 1099.
