She is a perfectly normal baby and you haven't done anything wrong. Both my DDs have been the same. At 11 months now DD2 still has never slept longer than 3 hrs. That's at night, during the day it's only 30 mins unless I hold her, which I do. But after she turned 1 DD1 began to improve a lot and was sleeping through at 18months. She was able to put herself to sleep at 2yrs. Maybe seems like a long time for others, but fine with me and she is a fantastic sleeper now. No troubles getting her to sleep or anything, she asks to go to bed when she's tired. Hang in there