Zoe, if you worked 12 hours last week, maybe they're still 'In Review' -- you can check in your Reports page. Perhaps they're only displayed in your profile when they move to 'Pending' later this week, but that's a guess.
Zoe, as Petra says, fixed-rate jobs are not counted by Upwork. The only way hours will show on your profile is if you have worked with the time tracker, or if you have manually entered your hours. The second option is not advisable unless you absolutely trust your client.
If you worked on a fixed-rate job, you should only have started work once your price had been agreed by your client and he/she had funded escrow with the full amount (or at least, for the first milestone).