This might be a better question for the delta forums.
I have moved on from Marlin / RAMPS boards for my delta, but at the time I recall G29 being for cartesian bed leveling not delta auto-calibration. I would consider reviewing the firmware for your printer to make sure you are using the correct g-code and parameters. You also will want to make sure the printer is dialed in a closely as possible before running the auto-calibration routine for the final tweaks.
Finally, what firmware are you using and consider attaching your config.h file so that others might be able to offer some assistance.