Upvote:1
You have asked a few questions; so I'll try to address your concerns:
Once you are inside the Schengen zone (that is, once you have arrived in Italy), there are no border controls so you can easily travel to Germany.
Your visa will be granted on the strength and merits of your application; so if you are applying for a dance workshop - then the relevant documents should be in order.
As far as the hotel reservation goes, yes you can change it later.
Upvote:2
You can make reasonable changes to your itinerary after the fact and a Schengen visa is in any case valid for the whole area (see e.g. Should my first trip be to the country which issued my Schengen Visa? but also Can I change my route and hotel reservation after getting a Schengen visa?).
But your question suggests you withheld some important facts and lied about your intentions. If you always planned to visit your boyfriend and submitted hotel bookings you never intended to use, that could be construed as fraud and it could have serious consequences if you are found out. If you just spend a couple of weeks in Germany and the dance workshop is still your main purpose, it's not so bad but there is always a risk.
In practice, because the visa is valid in Germany and there are no systematic border checks within the Schengen area, you're very likely to be OK but in principle you should have disclosed all your plans with the initial application.