Is the make-up fast valid if I hesitated in the intention, then firmed it up before sleeping, and doubted it after waking up?

The matter of intention is straightforward. Whoever thinks in their heart that they will fast tomorrow has made an intention. As long as you firmly intended to fast before sleeping, your intention is valid, and the sudden doubt does not affect the validity of your fast. Disregard this doubt and pay no attention to it, for this is one of the most effective ways to treat obsessive whispers.