I did this same thing and had no issue with level. I don't know what I did different, but I was 50 before BNK-3R. Have you done the first four rounds of each arena? Save the fifth of each for 2.5, but you can do the first four.
Edit: Also, did you do all green item or no item reward quests? You can do those. Just blue rewards and higher.
XBL GT: LazarusNecrosis The best techniques are passed on by the survivors. --Gaiden Shinji 1E 490