I love creating things from something "old" mainly bags from old shirts things that no longer have life and giving it life again. My son loves to help me with this.
i have this happend to me. when i did it it was because they were not really or to thin. i fine out that my beands will come off too. that because i got the worng Concrete. that how i learn out the hard way. i guessing you made them to thin. try agin ok. sorry i'm not much help. i'm just a borad house wife. lol good luck