Thinking of networking up the house, currently we have just got CAT6 cables coming through the walls, nothing professional or anything.

I was attempting to install a (CAT6 rated) faceplate in one of the rooms but couldn't for the life of me figure out why when I did a speed test, it would only get 100Mbps up and down instead of 200Mbps up and down. So after trying to wire it after the 5th time without success I decided to chop off the end and just put a plug on it and now I am getting the full speed.

Does anyone have a checklist of what is needed or should I rather just call a networking company to do the work for us? I don't mind doing it myself but need to know why I was experiencing the problem above, the current CAT6 cables in the house are T568A.