8 Transistor Full Adder
You've mixed up a few of your transistor types.  Here is the actual circuit taken from Arxiv



Generally you want to size the PMOS width to be 2.2X wider than the NMOS but here P! and P2 should be looked at closely. P2 will fight against N3 in series with N2 and P1 will fight against N1 and the low drive form the previous gate so I'd say that P1 and P2 width for a starting estimate should be about 1.1X of the width of N1,N3 and tune from there.

P3 and N5 should follow the 2.2X rule for width ratio.  Take All N's at minimum w &amp; L.