Trigger & Reset 555 same button
Well technically you can use an RC circuit to create a delay to when pin 2 is triggered but a better answer (I believe) is this after a little information: For the 555 timer to work properly, in either astable or monostable mode, pin 4 must be connected to positive voltage (at least 0.7 V according to Datasheet) prior to any input trigger voltage. This is because this reset pin works to disable the 555 timer when it’s held low. So a problem could arise if pin 4 (reset) is made high and pin 2 is made low at same time. To solve this problem, you’ll want to attached pin 4 to positive supply, and just use the pin 2 trigger as you were. When the pin 2 is high, your relay will be off, and only when pin 2 is triggered low, will the relay be on for the brief period determined by RC circuit attached to 555 timer. 

Also if you want to really want to give your piezo buzzer a 750ms on time, then you should consider removing the R1 and C1 connected to the nand gate. Instead connect the output of touch sensor to nand gate (connected as NOT gate like you have) then connect the output of that nand gate to pin 2 of a second 555 timer which is configured in monostable mode with RC network to give a 750ms period. Hope this helps.