My android phone is locked and is asking for my google mail Id but i do not...

...remember it, what should i do? My phone is an LG Optimus (Gt540) and I can remember the pattern code but it wont let me put it on, my screen comes up with 'Please use your gmail account to sign in' But i do not remember it. I have tried many times of the possibilites but nothing is working. Is there a way to get the pattern screen up again?
 
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