You absolutely don't have to change your whole self. And I’m sure you are nice.
And you can be both nice and quiet and a good leader.
But you can’t be a people pleaser and be a good leader.
You can’t shift your opinions dependent on who you are speaking to and be a good leader.
Leaders need to lead. And you can’t do that without have the courage of your own convictions.
You don’t have to be an extrovert, or loud, or mean. But you have to be sure about what you think, maintain good boundaries and set clear expectations for your staff. You also have to treat your staff fairly and equally.
If you are a new leader then no one expects you to be perfect at it straightaway- like most things it takes hard work and practice. But you can’t just throw up your hands and say “you are making me feel rubbish” anytime you get a bit of feedback - if you can’t take feedback or constructive criticism how will you learn or grow?
More to the point, as a leader you need to give feedback and constructive criticism to your team. The best and most effective teams operate 360 degree feedback loops so you will really need to learn.
Re-read your response to me, you asked for help and I spent my time offering some. You thanked me for it but you also tried to shut me down and make me feel guilty for giving it.
That’s not an effective strategy for personal development. It won’t work for your team or your boss.
“I’m too nice and sensitive to be asked to do things that make me uncomfortable” won’t help either. Learning new skills requires hard work and is often uncomfortable- that’s why you need to practice.
You need to take some ownership and responsibility. You said “somehow I have found myself in charge”. Somehow? Presumably you applied for the role, or at least accepted it when offered? Your boss gave you the role so has faith you can handle it. But to need to own it.
People don’t follow leaders because they like them, they follow them because they respect them.
Once you’ve earned the respect then they’ll like you. Sadly it doesn’t work the other way round. No one respects a doormat.