HDMI 5′ inch “dead zone” on touchscreen

Hello guys,

I’m making some tests with an rp3 and a Display 5” inch (800×480).

Everything works fine except for one peculiarity.
I have noticed that the calibration of the touchscreen I can not edit it in 99-calibration.conf, whether or not the file I tried to create it also and does not affect the calibration parameters that I introduce new.
I noticed that the display drivers modify my /boot/config.txt file and it is in this file that the “good” calibration parameters are supposed to be.
The problem basically is that when I touch the center of the screen the calibration works perfectly, the cursor is placed in the exact location. As I approach the edges of the screen, upper, lower and sides, the calibration is accumulating an error, and it is at the edge of the screen where I can’t touch or click anything.
Any ideas? I leave the config.txt to see if you see any parameter that is giving problems.
Sorry for my english, if you need information from some other file, ask me.
Thank you.

Code:
# For more options and information see
    # http://rpf.io/configtxtreadme
    # Some settings may impact device functionality. See link above for details

    # uncomment if you get no picture on HDMI for a default "safe" mode
    #hdmi_safe=1

    # uncomment this if your display has a black border of unused pixels visible
    # and your display can output without overscan
    #disable_overscan=1

    # uncomment the following to adjust overscan. Use positive numbers if console
    # goes off screen, and negative if there is too much border
    #overscan_left=16
    #overscan_right=16
    #overscan_top=16
    #overscan_bottom=16

    # uncomment to force a console size. By default it will be display's size minus
    # overscan.
    #framebuffer_width=1280
    #framebuffer_height=720

    # uncomment if hdmi display is not detected and composite is being output
    hdmi_force_hotplug=1

    # uncomment to force a specific HDMI mode (this will force VGA)
    hdmi_group=2
    hdmi_mode=87

    # uncomment to force a HDMI mode rather than DVI. This can make audio work in
    # DMT (computer monitor) modes
    #hdmi_drive=2

    # uncomment to increase signal to HDMI, if you have interference, blanking, or
    # no display
    #config_hdmi_boost=4

    # uncomment for composite PAL
    #sdtv_mode=2

    #uncomment to overclock the arm. 700 MHz is the default.
    #arm_freq=800

    # Uncomment some or all of these to enable the optional hardware interfaces
    dtparam=i2c_arm=on
    #dtparam=i2s=on
    dtparam=spi=on
    enable_uart=1
    # Uncomment this to enable the lirc-rpi module
    #dtoverlay=lirc-rpi

    # Additional overlays and parameters are documented /boot/overlays/README

    # Enable audio (loads snd_bcm2835)
    dtparam=audio=on
    max_usb_current=1
    hdmi_group=2
    hdmi_mode=87
    hdmi_mode=87
    hdmi_cvt 800 480 60 6 0 0 0
    dtoverlay=ads7846,cs=1,penirq=25,penirq_pull=2,speed=50000,keep_vref_on=0,s​wapxy=0,pmax=255,xohms=150,xmin=200,xmax=3900,ymin=200,ymax=3900