Can't get focus right!

Hi Dears : so having discovered I've been in auto focusing, when I thought I'd moved to manual, Please can someone tell me why I can't now get the focus right??.
I'm guessing that when the lens is at max zoom, then the positioning of objects is critical, so while the middle of these 3 wee Petunia's, that been flowering it's socks off all summer, is ok,other 2 ain't. Is that it??.
" Why do I always get the sticky end o fthe Lollipop" Marielyn M
Triage today said injury has activated Arthritis in my hip ( blast and damm ), it's clear on Xray, so keep exercising and hope it settles. The woman I saw was lovely : it helps!