It's about abortion, see notes below:

I got dosed by you and
(a reference to the mother taking poison to kill the fetus)
Closer than most to you and
(the closest anyone can get to another person is to be in their mothers womb)
What am I supposed to do
(the hopelessness of the fetus situation)
Take it away I never had it anyway
(the mothers view that once it’s gone she can pretend the baby never existed)
Take it away and everything will be okay

In you a star is born and
You cut a perfect form and
Someone forever warm
(the child feels originally safe secure and that the mother will be a place of warmth forever)

Lay on lay on lay on lay on
Lay on lay on lay on lay on
Way upon the mountain where she died
All I ever wanted was your life
Deep inside the canyon I can't hide
(even though the fetus is deep inside the mother it can’t hide)
All I ever wanted was your life
(all the baby ever wanted was to be part of the mother’s life)

Show love with no remorse and
Climb on to your seahorse and
(imagery is suggestive of the unborn fetus which looks like a seahorse in water)
This ride is right on course
(the babies life seems to be all planned out)
This is the way I wanted it to be with you (as if the the baby is imagining the life she could have had with its mother)
This is the way I knew that it would be with you

Lay on lay on lay on lay on
Lay on lay on lay on lay on
Way upon the mountain where she died
All I ever wanted was your life
Deep inside the canyon I can't hide
All I ever wanted was your life

I got dosed by you and
Closer than most to you and
What am I supposed to do
Take it away I never had it anyway
Take it away and everything will be okay

Way upon the mountain where she died (dying on a mountain symbolizes holding a position at all costs, which is fitting considering the fetus has no other place to go)
All I ever wanted was your life
Deep inside the canyon I can't hide
All I ever wanted was your life