Yep, I think that's what Mum thinks too. Interestingly she's quite happy with my other brother going by his shortened version!
Perhaps you need a name that has no obvious shortening or else one with short versions that you're happy with and work with your surname.
Kate, Claire, Anne, Sarah, Rachel, Iris, Ruth, Beth, Edith (although Edie is an obvious nn), Faith, Naomi, Hannah, Anna, Ruby, Zara and Phoebe are some I can think of off the top of my head.
Names that have a 'proper' end sound to them would prevent them from running into Leigh e.g. Imogen (nn Mo or Jen/Jenny), Miriam (nn Mim or Miri) or Harriet (nn Harrie/Hattie).
However, if Charlotte is the name you love then go for it and call her Charlotte for as long as you can - I went to school with a Charlotte who's never answered to anything else!