Yes. Ph.D. students need discipline. Many grad students cannot discipline themselves, resulting bad outcomes. (Luckily those students are smart enough to get though the undergraduate coursework very well. It seems you don't have the luck.) If you cannot discipline at the very beginning, you probably cannot gain yourself discipline in your graduate study. The graduate committee wants to get a discipline graduate student, not to train your discipline.
Getting a M.S. in statistics is good for you.