Dottie:

Check the chain that goes from your toilet trip lever to the new flapper.

If that chain is tight, it could be preventing the flapper from closing sufficiently to prevent any leaks.

There should be a clip on the end of the toilet trip lever that allows you to adjust the length of the chain to the flapper. There should be a bit of slack in that chain when the flapper is closed. If there's no slack in that chain, then you need to adjust the length of the chain to provide some slack in it when the flapper is closed.