Sorry but that plant does not look like RP OG#18.
The leaves should be a little thinner and all the true
OG#18s have nothing but purple stems starting from
day 1 all the way through to harvest. I have 3 growin
right now and I got mine from Cloneville.org. They are
in the SFV in LA and are very reputable and carry
clones from f1 strains mostly. All their clones are the real
deal no doubt. Calvin the owner is a very honest clone
expert/dealer with all the right stuff. Anyone that grows
or grew OG #!8 will tell you the same as my description
of RP OG#18. Medium wide leaves and all the stems and
branches are pure purple. I should be able to post some
updated close up pix of my RP OG#18's later today. Grown indoors
a little and mostly grown under the sun outdoors. They are
now in week 5 of flower. I the pic below they are in 1st week
of flower. Meanwhile here is a popular RP OG#18 grow thread and
you will see what I am talking about when it comes to OG #!8s.
https://www.rollitup.org/smoke-reports/299136-og-kush-18-reserva-privada.html