Why in lcd appear marks after using loca to stick the glass

I have broken two LG G2 using loca to stich the touch screen to it. I need help to understand what i am doing wrong.

After separating the broken touch screen from the lcd , i have cleaned the lcd and test it if works and it did. Then i have attached the new touch screen using loca (not too much , but it covered the lcd) . In the end i used UV to dry the glue and all it seems ok. I tested the phone and it was ok the touch working and the lcd had a clear display.

In the morning it appears some marks on the screen as shades at the corner of the lcd. I separated again the lcd from the touch because i thought cleaning the lcd will fix the problem but after testing the lcd was damaged permanently .

one doubt i have is that i have let enough the UV light dry the glue and had damaged the lcd. ( i have let under UV light about 1 minute).

Please help me because i am very new to this kind of thing but i need help.