File -> New\Restore -> I already have a seed -> Enter MultiBitHD seed, click options, select BIP39 -> set the derivation path as m/0'
Watch this: https://www.youtube.com/watch?v=E-KcY6KUVnY
I suspect the reason your current balance is off, is that you failed to export your "change address" private keys. Did you set the "offline" tool to use an "External/Internal" value of 1 to generate "change address" private keys?
This for "receive" addresses:
This for "change" addresses: