What purpose does くらいで serve in this sentence? How would you translate it?
If this were a written sentence, I would simply ask its author to rewrite it as it is not very clearly written. The 「思えないの」 ending, however, suggests that it is a spoken line, so I will try not to sound too judgy here.
Unless the larger context proves otherwise, the 「～～くらいで」 should describe how trivial, unimportant, etc. the preceding part (~~) is in comparison to what follows. Using the actual words, here is the structure of this "sentence".
"恋愛成就のお守りを託された was all that happened (which is quite trivial since a love charm is a hit-or-miss kind of thing) and I still do not think that it was 自己改革が出来る程度のもの."
"Sure, a love charm was left in my keeping, but who could have thought that it would be as super-effective as to make you accomplish self-reform? (Not me!)"