Absolutely fine mate.
Over the next few hours the yeast will start to react with the sugar and CO2 will be produced, making your bubbler 'bubble' like mad.
One tip of advice - in the instructions it states to top up after 3 days. You can do this if you like but BEWARE, the kit will bubble up through the bubbler and make a huge mess.
They have vastly overstated the initial ferment and I would hazard that the kit should be topped up HALF of the recommended volume 7 - 10 days AFTER the initial ferment, then the remaining volume a few days after that depending on the activity in the Demijohn.
I have done a number of Wilko kits and despite knowing how really over-presumptious the instructions are, I always get a messy brew. Albeit, less messy the more I leave it and the more i get used to them.
regards
WW