simple count of total correct

You can do it with a variable and a counter. I myself count the trials done correctly in my experiment and it looks like this:

In a block section:

block main
 set &mycounter 0
 message instone
 message insttwo
 message instthree
   tasklist
     koperta 5
end

In a task you add this line:

set &mycounter increase

I then prevent starting a new attempt until the previous one is done correctly by while. Set local var for 0 and make while loop like this: while $mytrial == 0 and change it only in CORRECT condition: 

if STATUS == CORRECT
set $mytrial 1

Of course, if you want the next attempt to start regardless of correctness, skip the loops with while and just add set &mycounter increase in the task section. At the end of task:
save &mycounter