LD1117 not providing fixed 3.3V
That's most likely the adjustable version. This is denoted by a lack of a voltage specified on the front - the 3.3V would typically have "LD33" printed on it. This is backed up by the fact that you appear to be powering the regulator from the 5V output of the Arduino board, and the no-load Vout of the regulator is ~0.7V below that.

Have a read of the datasheet, in particular page 12, "LD1117A adjustable: application note". It tells you precisely how to use just two resistors to set the voltage of the output to whatever it needs to be.

The maths involved isn't very difficult, but I do find that I'm always fighting a losing battle of what resistors I need vs. what I actually have in my pocket. To prevent you pulling even more hair out, take a look at this calculator and the associated table of voltages available using standard resistors. It's saved me hours of time! Don't worry that it's for the LM317, they're interchangeable as far as a basic voltage regulator goes.