It's normal to have anxiety while declining a role. It seems like you are failing to fulfill a commitment you made when you originally applied for the job, or that you are not upholding your part of a bargain.
Refusing a job offer will not cause problems if you conduct yourself in a respectful, courteous, and professional manner. Here are some pointers on how to politely reject a job offer:
You need not provide a specific reason, and the reason need not be the whole truth. At the same time, to decline a job offer politely, you do not want to say too little, or anything negative as you should take this opportunity to preserve the relationship for the future.
As soon as you decide to reject the job offer, you must first take immediate action and alert the recruiting manager or recruiter. Taking your time to update the employer of your decision is likely to create an inconvenience.
Although rejecting a job offer by email is permissible, speaking with the hiring manager or recruiter on the phone is a more respectful approach to do so. Additionally, a phone call provides a more personal touch.
In your email or call, start with a thank-you note like: “Thank you very much for offering me the opportunity to work at [Company] as [Job Title].”
“Thank you for your generous offer and the opportunity to work at [Company] as [Job Title].”