There are two contributing that first come to mind when it comes to building confidence and ‘taking a hold of the reins’ of leadership
Go back to establishing what your strengths are. Setting the boundaries you need and setting yourself up for success. It’s better to under promise and over deliver, even to yourself! Find ways that you know you can be helpful and do that for awhile, even if you’re not an official leader. Be a self starter and you will naturally grow into the leader you want to be.
You can also improve on your weaknesses by being willing to be less of a leader and more of a volunteer. Learn from others. No one knows everything so be open to stepping out of the leader position with the intention of learning a new skill or improving yourself.
If you work better solo rather than in a group you also have some great options to build confidence. If you’re feeling a bit shy speak to your local ‘official’ leader to see if there’s a project that you could work on by yourself.
These suggestions only work when you follow through, finish the task or work with a group successfully!