In no way, shape, or form is consuming any kind of cannabis a disqualification for a blood donation! Blood banks will only refuse intoxicated (cannabis, alcohol, etc.) potential donors. The reason donors cannot be high at the time of drawing is that blood banks disqualify candidates whose state compromises their ability to give an accurate medical history or legal consent.
So far, you’ve gotten the go-ahead to donate but been advised not to consume cannabis right before donation. Cannabis users ought to also beware, however, of ingesting immediately after donation, too. Whiting Out, recognized by paling skin and disorientation or fainting, may occur if users ingest cannabis within two hours of donating.