@imsak,
it's a bit awkward and vague.
This is how I'd write it:
Get an eyeful of this
: please let it rest that there is no such thing as an alien from
another planet coming to our earth.
however, what is vague is what you are telling the person ... to give what a rest? Give a rest to saying that there is no such thing or to stop saying that there is no such thing?