My server is hosted with BlueHost but not my domain. My domain is going to expire on the 28th of this month.
8 days... If you plan to keep that domain (why wouldn't you?) and the domain is registered with WordPress.COM as the registrar then contact them about renewing.
http://en.support.wordpress.com/domain-mapping/domain-management/
Once it's renewed then look at moving your domain to BlueHost if you want or if it's advantageous. If you can manage the DNS servers easily then why move it?
The reason I mentioned 8 days is that if you had the time then move the domain to your preferred registrar. But sometimes that takes a while (I'm moving a domain and 5 days later the transfer is still in progress) so I suggest you play safely and renew now.