I would 100% continue your plans to go!
I have already paid for my tour along with the accommodation in Paris as im going to spend more time there first.
I have a friend who works for Flight Center and i asked her if i should wait for the expo to book the Topdeck tour. She advised doing it now as its 10% off 2015 prices. She said the prices will go up and at the expo it wont be much of a saving for this tour and the exchange rate is so bad the 2016 prices will go up for sure. She did say booking tours and flights at the expo would be a good idea but she suggested the Topdeck tour was best to get now.
Dont worry hun, im the same about being nervous too, but at the same time i think its the bet adventure you could ever go on!