The likely cause is that your jetpack and battery aren't onboarded properly, which means the jetboard is still on restricting factory settings and not running on full power. To unlock it's full potential it needs to be onboarded (activated), see the steps below (or go to chapter Onboarding your jetboard and battery.)
ONBOARDING PROCEDURE
1) Carefully insert the fully-charged battery into your jetboard using the front and rear grips. do not attach the magnet key at this point. If you’ve also received a new jetpack, be sure to install it into the board before inserting the battery.
2) Download and sign into the Radinn app. Register as a new user or login to your existing account. Keep the device in hand and follow the steps outlined in the app.
3) When the board is connected to the app it will scan for firmware updates (see chapter "What is a firmware update for more). When the update is complete the jetpack and the battery will unlock.
4) Have more than one battery? Install the additional batteries and repeat steps 1-3.
5) Start making waves!
If you've executed the onboarding procedure and it's still running slow, try toggling the jetpack settings in the Radinn app - set the jetpack first to 'EASY' and then to the highest setting 'STANDARD' or 'PRO' depending on your configuration.