You're not triggering it right to attend your purposes. 555 requires to go low ( less than 1/3 VCC ) and back to high for triggering ( at least LM555 ).
You have to put a capacitor between the trigger input and the ground, forming a RC network with R1. So when you switch the power on, the capacitor will set the trigger less than 1/3 VCC while charging, providing the right trigger.
Will be better if you try it out on a protoboard.
Iuri~
EDIT: I forgot to mention, you need to put a resistor in parallel with the new capacitor, so when you power off the capacitor will discharge on this resistor. Beware, when the capacitor is full charged, the voltage on the trigger will be the value defined by the voltage divider formed by R1 and this new resistor and this voltage need to be higher than 1/3VCC. Also, depending on how fast you'll switch on/off, the discharging time of the capacitor has to be treated.
If you misunderstood something just let me know, and I will try to be more clear.
Iuri~