Please provide the code you ran so that we can more easily help you.
For now, maybe the code below will help clarify what's happening.
# Generate two density distributions with densities on the same x-scale
set.seed(5)
x1 = rnorm(1000, 0, 1)
x2 = rnorm(1000, 3, 1)
x1d = density(x1, from=-5, to=8)
x2d = density(x2, from=-5, to=8)
# Area under each curve is 1
sum(x1d$y * median(diff(x1d$x)))
#> [1] 1.000979
sum(x2d$y * median(diff(x2d$x)))
#> [1] 1.000978
plot(x1d, ylim=c(0, 0.45))
lines(x2d)
# Area under curve has doubled to 2 when we add the densities
lines(x1d$x, x1d$y + x2d$y, col="red")
# Renormalize so area under curve is 1
lines(x1d$x, (x1d$y + x2d$y)/2, col="blue", lwd=3)

Created on 2020-11-14 by the reprex package (v0.3.0)