How to send message to my channel using telethon

I'm trying to make my python script send messages to my private channel but I get this error.

telethon.errors.rpcerrorlist.ChatWriteForbiddenError: You can't write in this chat (caused by SendMessageRequest)

I'm only admin in that channel and here is code what I use for sending messages, when I try to send message to myself it works fine..

from telethon import TelegramClient
from telethon.errors import SessionPasswordNeededError

api_id = 'my api id'
api_hash = 'my api hash'
phone = 'my number'
username = 'my username'

# Create the client and connect
client = TelegramClient(username, api_id, api_hash)
client.start()
print("Client Created")
# Ensure you're authorized
if not client.is_user_authorized():
    client.send_code_request(phone)
    try:
        client.sign_in(phone, input('Enter the code: '))
    except SessionPasswordNeededError:
        client.sign_in(password=input('Password: '))

async def send_mess(message):
    await client.send_message(entity='my channel name', message=message)

while True:
    
    some other code

    if last_message != new_message:
        with client:
            client.loop.run_until_complete(send_mess(message=new_message))
        last_message = new_message

Do I need to change something to have admin rights on my script or where is the problem? I'll be glad for every answer. Gimme some good sample code guys :D this is really big problem for me now.