it would be great if you could post some pics of the system attached, as well as without the system so that we can see the quality of the bio hairline you are keeping....
as far as the white line....chances are she didn't allow the glue dry completely clear in between each coat and by laying one coat on top of the other it never got a chance to, this would also be why its lifting already...
personally positioning it lower than where it should be is a big no no....
concerning the edges....when you use tape it has to be done meticulously around the perimeter...when i do mine (using super tape) i make each piece meet end to end and it is exactly to the edge of the system... around the curved parts i trim the ends so that they butt up against the previous piece of tape....for a visual think of the way the corners of a picture frame meet. they are cut on an angle. of course i'm not doing it at a 90 degree angle because of curves, just trying to give you an idea of what i do...
it takes quite a bit of time but the edges are fairly undetectable, as undetectable as it can be with super tape which is a bit thick. but still one would have to really dig around to feel it.

its been my experience that when you go in for an attachment they are not as meticulous as they should be. i guess because its time consuming. they don't allow the glue time to cure and are not going for perfection. heck one time i had a tape attachment for the sides and back and the guy used 4 or 5 pieces that did not go completely around. there were big gaps between each piece of tape. not only that but it was so poorly done that when i got home i was able to effortlessly remove it!
this same person globbed glue along the hairline actually lifting the front edge to shove it underneath and pressed down! it wasnt until i left and ran my fingers along the hairline that i realized he had also left around a 1/4 inch of lace at the front!

regarding placing the system behind your natural hairline....it depends on its density and the style you are going for...if your hairline is thinnish it may not blended so well. you may see the system through it especially because its not graduated.

this is your first piece and you cant expect perfection...that sucks, i know.....
anyhow post some pics in the way i suggested above (wearing and not wearing) block out your face if you wish....then we can help you sort this out as best as possible.....afterward i would contact didi and let her know your dissatisfaction and hopefully she will rectify it