You don't need to have a booming voice.
As long as all the students can hear you, you don't need to have a deafening voice. This will vary according to the size of your classroom and the ambient noise, but normally your speaking voice needn't be a shout. When you need to get the class's attention, shouting can add to the noise and doesn't always help. Use alternative attention-getting techniques such as clapping, shushing, or raising your hand and clicking your fingers.
You don't need to be able to talk for half an hour straight.
In a modern EFL classroom, the teacher is not a lecturer but a facilitator. Yes, some speaking is required, but too much TTT (teacher talk time) is seen as counter-productive. The teacher is not in the spotlight all the time. Your job is to get the students to do as much of the work as possible!
You don't need to know everything in the world.
Students will ask you unexpected questions. Sometimes you won't know the answer off the top of your head and that's fine. There's no shame in having to look something up, and willingness to do some research sets a good example for your students.
Some introversion can be a good thing.
Quiet puts forward that introverts have a longer concentration span and are a more able to work alone than their extroverted counterparts. Teachers certainly need the self-powered perseverance to create a good lesson plan and source materials. I would say that a degree of introversion is actually essential for a teacher.
On the other hand, you do need some people skills.
It's important to be able to empathise with learners and establish a good rapport with them. The learners need to have some respect for you, and this may mean that you have to be assertive at times. Luckily, you can learn techniques to keep control without feeling like you're acting out of character. Ultimately, a gentle personality combined with effective classroom management can create a calm, productive classroom environment.
In all, don't be put off teaching just because you've been labelled as 'shy' by other people. By focussing on the learner and having enthusiasm for what you do, you can be an effective teacher whether you are naturally outgoing or not.
