For an actual psak you should go elsewhere, but here is how I see it:
Another point – if you’re a shomer of the money and you’re allowed to borrow it, does that make you a shomer sochor with the additional responsibility? If you do indeed borrow it, are you then a shoi’el with the even greater level of responsibility?
(Also, I don’t know if the halochas with being shomer tzedaka money differ from watching a friend’s money as far as shomer chinam etc.)