Our own galaxy, the Milky Way, is well over one hundred thousand light years across. We only see a pitiful portion of it. Although it contains several hundred billion stars in its expanse, we can only see a fraction of a fraction of them.
And even that doesn’t fully capture the essence of a galaxy, which also has planets, gas, dust, dark matter, and more. Galaxies are colossal objects, their true nature only becoming apparent to us a century ago.