Hopefully you'll improve with practice, but since you've "always had an extreme startle reflex" maybe you should have thought twice about keeping a BP. It helps to hold the mouse with the nose forward & sufficiently warmed so the snake can better target & hold onto it- BPs do rely on their heat-sensing pits, while any "motion" by the rodent should be subtle & never toward the snake. (Prey animals don't volunteer to be dinner, & such a bold action can scare off your snake, lol. The idea when offering prey is to elicit a slight "chase" from the snake.) And yes, if your snake refuses a meal, it's best to wait a week or so before offering again, so they aren't stressed about it.