The best in your situation is to use Synthetic urine or somebody else urine that yu know it's clean (yu can test it...).

The challenge will be to get ready to give the substitute sample without raising suspicion and that might requires some practice. Yu need to give it warm and I guess there is some trick for this. If you know the collection site, pay it a discrete visit and figure out how yu will play the trick.

Load your self with confidence, be calm don't be too nice just natural...

Best luck.