求英语作文,要求如下: 假如你是李明,你收到一封你的美国朋友Peter的邀请信.他邀请你去参加他周六的生日聚

求英语作文,要求如下: 假如你是李明,你收到一封你的美国朋友Peter的邀请信.他邀请你去参加他周六的生日聚
但是你不能参加.请写一封回信告诉他,你不能接受他的邀请的原因并致歉.词数80左右,要点提醒:1.感谢对方的邀请,并对你不能参加他的生日聚会表示遗憾.
2.阐述你不能去的原因
3.致歉并祝福

Dear Peter:
Hi!i am Liming.I am very happy when i received your invitation,but i have to tell you that i can not go to your party because Saturday is my grandma`s birthday too,i had promised my grandma i will go to her house and held a party for her.So,i am sorry,i can not go to your birthday party,and thanks for your invitation.Don`t worry,i will send you a gift on saturday,and i will miss you every day and every night.
Yours sincerely
Liming