I see that the question is already a bit old, but for others with the same question:
In FL Studio it's best to use edison when saving samples so you can clean up your sample (you can also delete or add loop points in edison). After saving a sample and throwing it back in FL, you can change the root note in the envelope tab. (Click on your sample in the pattern view and go to the second tab) FL's default root note is C, but when you have a sample at D, you can change it to D3 for example so that your sample is at D3 in the piano roll.