The scissors-type slides always leave some of the exterior siding in the interior, since the scissors don't fully collapse. If you peel back the carpet on the bottom of the front of the slide, you can better see if it is seating properly. You can also use a mirror to see if the scissors look fully collapsed, from the left side.
However, if it isn't like it was, it probably isn't right.
BTW, several people have taken measurements at the corners of the slide (distance to interior wall). Mine, like others, doesn't seen to match exactly, but is always the same each time. The seal looks good, and it is seating well. That slide always seems to freak people out, at first.
2003 Alpine 40FDTS (400HP)
Long Beach, CA