First off, sorry that no one got to this sooner, but congratulations on 60 subscribers!
Now to answer your question, if you go to YouTube and click this button:
and then select where it says "milestones" it will show an achievement certificate of any recent milestones you have accomplished. Then if you want to print it, you can click on the certificate and then click the green button that says "download certificate". Then you should be able to open the image that was downloaded and print it from there.
You can also just save the image and upload it to your subscriber achievement thread (this thread), so that you can show that you have reached this mile stone, since you are actually supposed to attach your certificate when announcing you have reached a channel milestone (like number of views, or videos uploaded) or a subscriber milestone (showing you reached a certain amount of subscribers)