Use the reference designators to tell us which LEDs (and other parts) you have in the circuit. Note that as you add LEDs in series, the minimum operating voltage goes up. Depending on the exact LED part number, each LED adds approx 1.8-2.0 V.
AND - If you have only one LED in a string, you should not run the circuit at the full 9 V. At 9 V and only one LED, the LED current will be around 90 mA. A bipolar 555 can sink this with no problem, but the LED might fail due to overheating.
Suggestion: Start with a 6 V battery and one LED string with one resistor and two LEDs in series in it. R2, D1, D2. This should blink safely. Now you can mess with R1 and C1 to get the blink rate you want. Once everything is happy, add D3 and D4 to the string and change the battery to 9 V. Blink rate should be the same. At this point you are running approx 11 mA through the LEDs; very safe, but the LEDs will be a bit dimmer than before. Adding the other strings will increase the battery current but shouldn't change the brightness of the individual LEDs much.
With the circuit as shown in the schematic, the current in each LED is approx 10-11 mA. If you want more brightness (with shorter battery life), you can reduce R2 - R6 to as low as 39 ohms. This yields around 20 mA current per string, a common "full brightness" value for low cost generic LEDs. At this point the 555 is sinking 100 mA, so its low output voltage will be higher than before. That 100 mA probably is a high estimate, but safe.
ak