Relax. The urine test is a cheapo (you dont think the CAA do expensive tests do you!?) to test you for blood in the urine, diabetes etc. You can do EM scanning for drugs on the urine but it is expensive, takes weeks and isnt done.
So relax - I did my initial at Gatwick a day after being covered in cocaine (I am a doctor and use more cocaine than your usual Columbian drug baron, but I completed my medical LPC so it is legal!) and they didnt bat an eyelid. Rather different from trying to get through Miami one day, but that is another story....
The longer term issue is that it is very difficult to buy the pure drugs I use on the street. You are more likely to buy unpredictable isomers - or worse - which can have an effect on your brain for days and days. So please keep your recreation and your future flying very separate.