I'd say if you're making generic hearts and other rounded shapes, just decorate what you have. No one will notice that the heart is bigger than the cutter. But, if they're shapes that are more unique and depend on the dough holding its shape so you can recognize the cookie shape, then you may want to re-bake. Sounds like you don't have a well formulated dough though, if your results are as variable as you say. So you may want to spend time trying other recipes (if you have the time) before you re-bake.
My recipe is very consistent; it has a mixture of butter and shortening, so it spreads less than it would if all butter. If I want no spread with it, I must cut back on the leavening though (but this has trade-offs - denser, pastier cookie).