Is avoiding sins out of fear of the self-imposed punishments I have decreed for myself, not out of fear of God's punishment, considered correct in terms of intention and drawing closer to God?

There is no impediment to punishing oneself for committing sins or falling short in duties, provided that this does not result in certain or probable harm to one's health, based on the Prophet's (peace be upon him) saying: "There should be no harm nor reciprocating harm." Therefore, punishing oneself by eating hot peppers and refraining from drinking water or food for an hour, if it harms one's health, is impermissible. As for doubt concerning the intention, pay no mind to it, for your motivation is the fear of Allah and the encouragement of your soul towards acts of obedience.