I laid down attached pad carpet in the basement. I have a Kanga carpet
wall trimmer tool.

The attached pad makes it very difficult to crease the carpet against
the wall. Therefore I can't determine the right line to trim the
carpet.

Further, because of the attached pad, it's very difficult to shove the
carpet wall trimmer against the baseboard. Thus, even if I could
crease the carpet correctly, it's very tough to trim the correct
line.

Any advice?

I already screwed up one wall. The carpet is 1/2" to 5/8" away from
it, after I struggled with the situations described above.

I can't believe I was so stupid to attempt this install myself. With
the Home Depot $37 install special, I could have had regular carpet
for only a few hundred more.