Calling the BB on the turn when you need a "miracle" card
could certainly be contributing to your breakeven state if,
by miracle card, you are referring to a card where you lack
the proper implied odds to make the call.

If you did this on 1% of your hands (which I recognize is
probably a bit high), it could have cost you a fair bit.

Assuming you lost all the hands requiring a miracle card,
you would have been +700 for having folded when you lacked
the odds to call.

Allowing for the fact that you probably hit the card occasionally,
maybe 15/350, and won an 8BB pot each time, you'd still be
+430 for having not made the turn calls.

I had a similar leak at 1/2 where I was overestimating the
eventual pot size so that I would have the implied odds I
needed to call on the turn; when I stopped, my BB/100
started to inflate and in short order I was doing well at
2/4.