Would it better to say ,”I am getting better and better at maths “ rather than “I am excellent

Added 3+ months ago:

In Psychology, it is a well-known fact that one can change oneself through positive self-affirmation & visualisation .It is believed that the self-affirmations to the subconscious mind is best done in an “already achieved mode”. For example, a student who is weak in mathematics and wish to improve on it should say the self-affirmations as “I am excellent at mathematics” & also visualize himself as ALREADY being good at Maths repeatedly. Or a person who is a coward could reprogram his mind by saying to himself,” I am brave”, etc. This is so that the subconscious mind is set with the positive intended goal and thus will program the whole body with the message. But the question is that such self-affirmation is not the truth (or not the truth yet). When he is telling himself that he is ALREADY being good at Maths, he is actually “lying “to himself.
So, would it better to say,”I am getting better and better at maths “rather than “I am excellent at maths”?