Hi! Looked for answers but never quite found what I needed...

A nosy onlooker unscrewed the cap of a finished bottle of our syrup I'm keeping in the freezer/fridge for a gift later this year. I'm worried, given the amount of care we put into sanitizing everything, that I can't just screw the cap back on, since it was open the better part of a day without my knowledge.

My question is this: can/should I reboil that particular large bottle of syrup, either in its current bottle (through double-boiling or some such) or apart from it? Will that effectively kill whatever bacteria might have gotten into it? Or am I being too worrisome? thanks!!