Is making a vow wrong, and is repentance accepted only for sins that have wronged oneself?

Allah Almighty accepts the repentance of His servants and rejoices in it, no matter how great the sin; for sincere repentance erases what came before it. Your taking a vow is a disliked mistake, and your vow to abandon the forbidden is not considered binding by most scholars. If it were binding, then you would owe an expiation for breaking an oath upon returning to sins. It is more befitting to use the body in obedience to Allah and to show gratitude for His blessings, which are removed by sins.