Why not e -mail Debbie for some advice on what would be safest/best in the circumstances? I`m sure she`d help. While I`m no fan of legal-eagles, I`m sure there are ones which would take your case on a `no-win, no-fee`` basis....... clearly, to my mind, you have been a victim of negligence.
I wouldn`t leave a lot of excess lace at the front... it will attract dust/dirt etc to the adhesive/tape under it and will become obvious to the eye.... if you like, leave 2 or 3 millimeters and see how you get on..you can trim it back to the hair when you de-bond it if it`s too visible etc... personally I trim back to the hair.......just take your time...all I do is [ i`m right-handed] sit the system in front of me side-on..[the back/nape part is on my left, the front is on the right] I then catch the front hair in a bunch just at the temple area with my thumb directly in front of and holding/folding back the extreme front hairs which clearly allows visibility of the excess lace. I then start my trim-off, carefully keeping the scissors in front of /`parallel ` with the hairline. Just simply move the thumb around towards the other temple-point while holding the hair back off the lace so you can see clearly ....if you imagine the front hairline [ bird`s eye view] as horse-shoe shaped, you are simply following that shape with your scissors albeit maybe 2 millimeters in front of the hair itself.....hope that helps... regards for now, Paul.