Is the card (the work) capable of copyright protection (here we are referring to the card in its entirety, including all the content)?
The correct answer is that you have created an artistic work capable of copyright protection because it’s original and you didn’t copy it substantially (you may have taken small quotes etc which may be deemed insubstantial) from anywhere else. You may have been provided with ideas e.g. the card having a particular theme such as a champagne bottle on the front, a verse inside, but there is no copyright in ideas.
The work is original (not copied from anywhere else), but does not need to be novel e.g. a completely new idea. In the UK there is no formal registration process, nor is it a requirement to stamp it with the © symbol, year of publication, name of copyright holder. If you want to know more about what is protected by copyright please read: Categories of works and periods of protection. If you want to know more about how you get to own copyright please read: Who owns copyright in a work? and Do I have to pay a fee and register Copyright?