R1/R4 make a voltage divider that splits the voltage between the supply and C1 voltage. As R4 is the lower leg, the gate will reach the threshold earlier. Try changing R1 instead and you should see the desired results. BTW, I think you have the gate and anode reversed.
A tip so you get quicker responses, when drawing diagrams follow simple rules,
1. Power (+) is the top line.
2. Gnd (-) is the bottom line.
3. Supply is on the left.
4. Try to keep components in the direction of current flow. (R1, R4 & C1 vertical and SCR pointing down)
Following these simple rules will enable people to understand your diagram in seconds and make them more likely to respond. To understand your diagram, I had to rotate and flip it - see attached.
Mike.