Hi Mary, it is funny but "move from your center" might mean different things to people (there's lots of diversity in aikido).
So whatever advice you get here may be NOT what your teacher is looking for.. but who knows till you play with it.
If you are going to play with things, there's a nice grab bag of advice in this thread. I also suggest thinking about the breathing practice on aikidojournal.com written by Mike Sigman about "Putting ki back in aikido practice." (Can't find the link b/c aikido journal seems to be down right now) But that will be something to work on every day for a long time, not
something that will help you right now.
I second what Lee and Ahmad said. With Lee's trick of pushing something heavy, after you experiement with what he said, you can rehearse the correct feeling later. Pretend to push the thing, and pretend to spread the feeling out. Since you are pretending, you don't have to flex a single muscle (you could be laying in bed). But even so, the ki will do what you are pretending. With Ahmad's baby-holding trick, you can do that at home when you can take your time and not worry about a partner. And it could be a bag of bricks as well as a baby-- just concentrate on feeling that weight bearing down on you (in your mind.. again, pretending), and letting it stack on the ground through you, rather than you straining to lift it.
Anyway... good luck. And if what I (or anyone) is saying doesn't work or confuses you.. that'll teach you to take advice on the net!
j/k, I really hope it helps.