The urine test does not detect THC.
It looks for metabolites.

Thc is stored in fatty tissues in your body,
Whenever those fats are converted to energy, metabolites are created and eliminated, through the kidneys mostly.
Any excess fats that are ingested will have no effect on your test results.

The most effective method, is abstinence, for about a month in most folks.
Try to come up with a legitimate excuse to postpone the test.

Or, buy a test kit from the drugstore and test yourself just prior.
If you flunk, substitution is advised.

I'm no expert, so hang out, until you hear from Burnt toast.

Aloha,
Weezard