Number Pad's Numbers Flipped on Touchscreen

Of course it will. I just invented a descriptive name out of nowhere.
You would need to declare the variables e.g.

int pixel_x, pixel_y;      //declare the variables before they are used

 if (p.z > MINPRESSURE && p.z < MAXPRESSURE) {
    // scale from 0->1023 to tft.width
    pixel_x = map(p.x, TS_LEFT, TS_RIGHT, 0, tft.width());  //map left->right as 0-239
    pixel_y = map(p.y, TS_TOP, TS_BOT, 0, tft.height()); //map top->bot as 0-319
    ...

My main point was to say that TS_MINX is a silly concept.
You want to think about LEFT and RIGHT. Sometimes LEFT will be less than RIGHT. Other Touch panels might have LEFT more than RIGHT.

You want to map LEFT and RIGHT to pixel X coordinates. You just put in your calibration values and the map() fuction does the correct transformation.

David.