I am vacuum bagging the hull of a boat and the sealing tape isn't sticking well to the fibreglass.  The fibreglass was laid 7 days ago. I have tried washing thoroughly with acetone and also a light sand, but tape is still not creating a good seal.  Any suggestions?  Does the fibreglass need to cure longer? Any assistance would be appreciated.

Age can also be an issue, bagging tape does expire and it loses its tackiness the older it gets. But realistically, it lasts for years, so this would only be a concern if you've had it for many years.

It does sound more like you haven't spent enough time pressing it down to make sure of the seal.