Turning down a job offer

Recently I received a job offer for a position I've applied for. I've re-considered and I'd like to turn down the offer.

I'm planning to send an email to a lady there who interviewed me but I don't know how to politely say that. Basically I'd like to say that I'm grateful for the opportunity but at this stage the job is not right for me. If anyone has any ideas on how to express this in Japanese I would appreciate it.
Thanks in advance!

How about this?

このたびはありがとうございました。面接時、(interviewer's name)様に親切にしていただいたことは一生忘れません。しかし、この仕事についてあらためて考えた結果、私には適性がないと判断し、勝手ながら、辞退させていただくことにいたします。
(interviewer's name)様の今後のご活躍と成功をお祈りいたしております。

That's fantastic! Thanks very much for your help.