I just redraw the board and used 8mil for clearance
Ground plane - draw a polygon (not a rectangle) around the outside of the Dimension line. Name it Gnd. Do the same for both Top and Bottom layers. Then click Rats Nest and it will connect the Gnd pins to it. You may need to add a few Vias, aslo Name them Gnd, to connect the Top & Bottom layers for maximum Gnd plane coverage.
You're using the SSOP package, with 0.65mm pitch on the pins? That could be tricky soldering.The '328P in TQFP with 0.8mm pitch is hard enough.Ground plane is definitely useful.
i never used ground plane, i don't know how to make it
I don't understand, What does '328P have to do with my shield?