At the moment you can back out and all it will cost you is £99.
An early bird reservation gives you a first refusal when a plot is released for sale and the price is decided.
It could have been far higher than the prices of similar homes at the time you early birded.
Whether legally or morally correct or allowed" quite frankly, these unregulated plc housebuilders can and do, pretty much whatever they like with little chance of any punishment coming their way.
I know of one couple who were in their late 70s, did and early bird reservation, agreed the price on release and had their sale withdrawn because they were just 2 days late exchanging on what was at that time, a far from finished house.
Just a week later it was reserved at £5,000 higher price to someone else. This was 20 years ago!
Whatever Bovis have now decided to do, you have clearly been given insufficient time or notice to exchange contracts and should at the very least not be out of pocket.
You should also rejoice in the fact that you will not be buying a Bovis Home!
Please Google: "Problems with Bovis homes" 133,000 results!