Definitely not! There is every chance the beer will gas up over time. Be patient.

The most common causes of flat beer are as follows :
* Not enough time has elapsed for the beer to mature in the bottle
* Bottles stored at low temperature impeding secondary fermentation
* None or insufficient an amount of priming sugar added to the bottle
* The bottle cap has not been clamped on securely
* The sterilising liquid has not been thoroughly rinsed from the bottles
* The brew has been left in the fermenter too long after completion of fermentation.