Just go with the flow.....Use who you want. if you can't use em yet. maybe after using another character u'll gradually get better at ur fundamentals and if you go back to ur initial character, u'll might not feel the difficulty.
I know someone who couldn't start BB with rachel , played around with the whole roster , settled with Hazama and Hakumen - thought "why not go back to rachel"
He settled with her Better than he did b4.
Not saying that'll work with everyone but...idk....its up to you in the end....I just mash buttons ... meh... Fundamentals + practice .. you can do it man.