Ringing in the output of 555 timer
First, make sure your 555 timer can handle a supply of 9 V.

Second, check how your scope probe is grounded.  My guess is that you either left the ground floating, or connected it in the wrong place, like back at the power supply.  Hold the scope probe ground clip right on the ground pin of the 555, and the tip right on the output pin.  Most likely, you will see much less ringing.

In general, you have to pay attention to details in engineering.  Your "Eh, who cares" attitude has no place here.  In one small question you missed two important details already, with C3 being shown as 100 mF and the frequency being stated as 10 Kelvin-Hertz.  Properly grounding the scope probe is another one of those details that matters.