Your contract of employment, which you probably signed when you took your job will define the notice period on both sides. You give three they give you three, or pay you in lieu.
Although I am not commenting on your particular circumstances, the reason many companies now have a three month notice is that it can easily take three months to replace you. And if you work a shift rota as you probably do, to let you go before the end of your notice may place hardships on your colleagues, particularly if you work in a small outfit.
My advice would be to try and negotiate your way out of it by asking if they are prepared to let you go as soon as your replacement is found, you never know maybe you can get away in six.