You will not be able to receive your second dose sooner than the minimum interval (currently 21 days) after your first dose. It is important that you do not wait more than 84 days after your first dose for your second dose. This is as per guidance from the World Health Organization.
If you have access to the Internet, and the second appointment you receive does not suit you, you can choose when and where to get the second vaccine or change your vaccination appointment. To do this: