Hi Julie. That does seem to be a high bill. The standard B Gas tariff for average consumption of 20,500Kwh produces a current average bill across the country of £525 a year. Please note that this amount is an average across all regions so there may be a slight variation for your area. It is also based on current prices so it is not a perfect fit with your 9 week period which would include some weeks at a higher tariff before the recent price falls. If you have a duel fuel arrangement with B Gas the amount would rise to £835 for their standard tariff.
The usage that you have indicated seems to imply that you should be close to average but you can check this against the consumption noted on your bill.
Other things that you can do
Check what tariff you are on.There are other higher B Gas tariffs . Your tariff should be clearly stated on the bill. If its an expensive one consider changing tariffs if you want to stay with B Gas or change supplier if there is a better product for your area.
Was a correct reading was made when you moved into the house? The bill should say if it was a customer reading or an estimate.
If it was a customer reading was it one that you gave them?
Was the last reading an esimate? Again the bill should be clear on this point, if it was check your current meter reading against the figure on the bill and if there is a big difference give B Gas a call and ask for an adjustment in the bill

Good luck and please do not hesitate to post another message if you cannot resolve this.

Paul