You try and avoid too much lime with potatoes because it is thought to encourage scab, a disease with corky like growths on the outside of the potato which does not affect the eating quality, but doesn't look very attractive!
If you have already planted, I don't think there is a lot you can do, except maybe use grass clippings to earth up, as using that is believed to help prevent scab. Mushroon compost varies widely in the quantity of lime it contains, you might be lucky and have some with so little it doesn't affect them at all.
