If you just accidentally put different fuel in your fuel tank once, you wouldn’t have to worry too much about it. However, it is not recommended to do it regularly since every car engine was designed to burn a specific fuel. Putting different fuel regularly may lead to serious damage to your engine in the long term.
The information in this answer is general in nature and is not legal or insurance advice for your specific situation. Policy language varies carrier by carrier; your declarations page is the final word. If you're unsure, call your agent before you need to file.