Hi Marie and welcome to GoY. I take it this is exactly what you have done... potted up an Acer using regular compost rather than ericaceous. Nothing is going to 'happen' though you might want to give the tree an ericaceous feed. We have several Acers in the ground and our soil is just about neutral - doesn't have any effect on them. What they seriously don't like is being exposes to a lot of wind and full sun.

Nothing, as Moongrower says, Acers don't need acid soil, they just don't like limey soil.

I thought for years that they needed ericaceous soil. However, normal compost (multi-purpose etc) from a Garden Centre or supermarket is neutral so will be absolutely fine :O) Welcome to Grows on You Marie! Karen