Hi,
another user posted a similar question: How to randomize feedback or create conditional feedback
If you look at my response I think the same logic can be applied in your case.
You can determine if the trial is a small or a big one based on a colum name.
As for showing the feedback only in the first 3 trials you can have a counter that starts at 0 and goes up by one when a small trial is presented and is resetted to 0 at the end of the block.
You can than not show the feedback for small trials after the first three in different ways, i think the easiest is to end the routine with “continueRoutine = False”.