The good thing is that your chalk addition was probably ineffective, since it wouldn't have dissolved in the mash. But that brings up the question of why you were targeting such a high bicarbonate content? I can't think of any mash that would need that bicarbonate content in the water.
The pH reading is reassuring, assuming that it was obtained from a room-temperature wort sample using a freshly-calibrated pH meter. In that case, you probably don't have much to worry about.