Why am I not able to receive service on my phone?

I've done a replacement of my LCD and back cover on my AT&T iphone 4 and I am unable to receive service. When I was on the highway was actually getting service but at work I had no service it just kept saying searching. Now i've come home reopened and made sure everything is in the right spot and now i'm getting 1-2 bars. I've read multiple answers on here to try to fix it but nothing is working. Everything looks fine and in place. The only thing i'm concerned about is one small piece that i'm not sure where it goes. It would be greatly appreciated if anybody can help.

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