Help with a couple calibration questions?

My Ox CNC is getting closer (i think). I calibrated the x,y and z axis this weekend. I feel like the movement is pretty spot on. However, I did a test circle with a sharpie and my circle didn't quite close. Below is a link to a pic I took. I'm only worried about the part where the drawing started and ended. I haven't leveled my spoiler board yet. Circle with Pen:IMG_3112.JPG

Also, I used a 3/4 diameter double flute to drill some holes in my MDF to use for holding work in place. As it was drilling the holes, I noticed the z axis would tilt very slightly as it began moving down into the wood. When the z axis finished and began raising, it would clear out the hole. Therefore when I put the dowel in, there's a small bit of separation in the front as you can see in this pic: IMG_3113.JPG

It repeated this on every hole. Is this considered Backlash? Is there anything I can do to correct this? There's no wiggle on the z axis, so I don't think anything is loose.

I use Universal G Code Sender. I don't believe there is a backlash adjustment available within it that I'm aware of.

Below are my current GRBL settings. I would really appreciate any help or suggestions. Thanks!!

GRBL Setting:

$0=10 (step pulse, usec)
$1=255 (step idle delay, msec)
$2=0 (step port invert mask:00000000)
$3=2 (dir port invert mask:00000010)
$4=1 (step enable invert, bool)
$5=0 (limit pins invert, bool)
$6=0 (probe pin invert, bool)
$10=3 (status report mask:00000011)
$11=0.020 (junction deviation, mm)
$12=0.002 (arc tolerance, mm)
$13=0 (report inches, bool)
$20=0 (soft limits, bool)
$21=0 (hard limits, bool)
$22=1 (homing cycle, bool)
$23=0 (homing dir invert mask:00000000)
$24=500.000 (homing feed, mm/min)
$25=3000.000 (homing seek, mm/min)
$26=244 (homing debounce, msec)
$27=5.000 (homing pull-off, mm)
$100=27.000 (x, step/mm)
$101=26.634 (y, step/mm)
$102=202.000 (z, step/mm)
$110=4000.000 (x max rate, mm/min)
$111=3000.000 (y max rate, mm/min)
$112=1000.000 (z max rate, mm/min)
$120=2000.000 (x accel, mm/sec^2)
$121=2000.000 (y accel, mm/sec^2)
$122=1000.000 (z accel, mm/sec^2)
$130=1190.000 (x max travel, mm)
$131=569.220 (y max travel, mm)
$132=1000.000 (z max travel, mm)