Hello, Anne and thanks for your question.
If you did not yet receive your letter of approval with your Precheck KTN (Known Traveler Number), it sometimes takes a few days or a few weeks, to receive this, after your interview.
For the moment, you can check the following two sources, to see if you are already in the system, a number has been assigned and you just didn't receive the approval letter, yet:
You can call the Universal Enrollment Service at: 855 - 347 - 8371
(Hours are Mon. - Fri. 8AM - 10PM, Eastern time), or, you can visit the website below, and fill in all the requested information:
I hope you are able to retrieve the number and use it on your flight on Thursday!
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