Let us make = `asah (Strong's)
1) to do, fashion, accomplish, make
a) (Qal)
1) to do, work, make, produce
a) to do
b) to work
c) to deal (with)
d) to act, act with effect, effect
2) to make
a) to make
b) to produce
c) to prepare
d) to make (an offering)
e) to attend to, put in order
f) to observe, celebrate
g) to acquire (property)
h) to appoint, ordain, institute
i) to bring about
j) to use
k) to spend, pass
b) (Niphal)
1) to be done
2) to be made
3) to be produced
4) to be offered
5) to be observed
6) to be used
c) (Pual) to be made
2) (Piel) to press, squeeze
I don't see anything that justifies "let us make" as a plural.
It isn't uncommon for the KJV translators to insert their theology from time to time. You can also see it in the way italicized words are used and translated.
I gave the Hebrew and the translation of the Hebrews, the Jews. They are not KJV translators, and Strong's doesn't apply!