I cannot know without seeing you practise, but the question itself says you are not confident, and confidence is the whole point of the symbols. They were added to the system of Reiki to give people something tangible to draw, say and chant so they could feel the energy. They are there to support you, not to be worried about. Practise what you were taught and let it take you in.

The second symbol and its mantra. In the West it was labelled mental and emotional healing. In Japan the mantra means our natural inclination, and our natural inclination is to be our true self. Its characteristic is harmony: the balance between earth and heaven in which we start to feel what we really are.

There are two answers. A person who practises a healing method is a reiyōshi. But the memorial stone of Mikao Usui describes him as someone who undertook shugyō, committed training, and a person on that path is a shugyōsha. From a Japanese perspective that is the better word for a Reiki practitioner: someone committed to daily self-practice, not someone with a certificate.

Chakras came into Western Reiki from the New Age movement and have nothing to do with the Japanese system. Teaching from a Japanese perspective, I work instead with Sanmitsu, which I call the Three Diamonds: body, mind, and the breath that links them. Those three sit at the base of every practice in the system.

Strictly, the precepts are the foundation of the system of Reiki from a Japanese perspective. Meditation is how we become the precepts: contemplating the waka poetry, practising Joshin Kokyu Ho, breathing into the hara and letting awareness expand until we feel our interconnection with everything.