PuTTy and other SSH clients are simply a way to connect to the OpenSSH daemon on your Droplet. It doesn't matter which client you used to set up your Droplet, so you should be able to access it from your macbook as well.
However, if you generated the SSH key using PuTTygen, you will need to convert it to the OpenSSH format as PuTTy saves its private keys in its own format. In order to do that, open your PuTTy key in PuTTygen and click on Export OpenSSH under Conversions. Then, transfer the resulting file to your macbook.
You can use it by passing it along with
-i to the
ssh command, like this:
ssh -i /path/to/exported/key user@ip
Or, move it to
~/.ssh/id_rsa, making sure that you don't overwrite any existing key that you might already have and need, and
ssh should automatically pick it up and use it without having to pass the
-i option to it.