I got to thinking last night about my role as a game designer. This was brought on by the absolutely fabulous Pyramid Arcade which is like a treasure-trove of board-game (and more) designing tools. That got me thinking of the title of "Game Designer". Honestly I've been tinkering wit various game designs for (mumble mumble) decade(s). That got me thinking about what point one can call themselves a game designer.
Short answer: Whenever you've worked on designing a game.
That might seem like radical thinking to some but it's true. It's the same if you're a writer, programmer, artist, or any other creative field. Once you've started with the intention "I'm going to do X" then you're X. Doesn't matter if you're doing it well, poorly, professionally, or amateurishly. When you go with the intention to do X you're X.
Now, you can choose to shirt that role if you want (I'm not a game designer). That's your choice and right. But if someone tells you that you need to do some other work in order to achieve the title of game designer then you can tell them to stuff it.
This is my periodic reminder to myself that even if I'm not a great game designer I'm still a game designer, full stop. Hopefully it'll help you uncork whatever creative juices you may have and allow them to flow despite the self-doubt you may be facing.