S.B.
I think that if you have any doubts about it, you shouldn't do it.
I'm not against adoption, exactly the opposite, but if you are worried about an adopted child upsetting the family dynamic any more than you would worry about your own new natural baby doing so, don't do it.
There is nothing wrong with not being cut out for adoption.
Just reading your post, no offense, it's clear you worry more about the affect it would have on your family than you are thinking about what you have to offer a child for a lifetime.
A child who has already been given up should go to someone with no doubts.
I have adopted friends and people in my family and if you're not prepared to know with all your heart this is the right thing, you shouldn't consider it.
Adopted children need unconditional love more than anybody.
They really do.
If you're not prepared to give that it doesn't make you a bad person.