Q.Is Oak leaves ok for mulch for my new pineapple guava?
Just planted it in a half barrel and put manure in the bottom. Plant is only about18″
tall, am I going to kill it. one article said no manure. Just planted it today. Replant it?

The oak leaves mulch is fine.
Potting soil should not be in layers (except for the mulch), its should homogenous. I would not have recommended the layer of manure at the bottom of the container. It is a harsh, high salts fertilizer, especially if fresh/raw, un-aged, un-composted.
I would advise re-potting it and use the manure in your compost pile. If the manure is aged, you can mix it in with the potting soil, but not more than about 5% of the volume. Fertilize the pineapple guava with a slow release natural fertiizer after it shows some new growth.