If 3g is turned on its effecting my phone signal

I recently changed my front and back screen. Now I am familiar with i4 so it was my first 4s. Since it was done my wireless and 3g seem to be constantly hoping to wireless then 3g then E and sometimes nothing. Each time it changes which is regular you can visibly see the phone signal blanking out and interfeering with calls where they can here me but there speech is broken like your on hold briefly. I think i have it pinned to turning off 3g as you can see when you turn it on the signal goes straight away and when off it comes back again and i can make calls fine. Its really weird. One thing i know is i have the grounding finger the wrong way around as in facing in like turning it right pushed in against the motherboard rather than the framew of the phone as in the pictures so maybe this has something to do with it? everything else went fine although i have a small straigth piece of rubber that came out when lifting the board and not sure if its cosmetic or not?? it seemed to be under the top right of the board where the antenna is? any help would be welcome. Also do the black pieces of tape need to be put back. i assumed they were just a way of them knowing you were at it?