There is no such thing as the "Baltic Peninsula". If you mean the Balkan Peninsula, it is made up of 11 countries:
Norway and Sweden
Norway and Sweden
Sweden and Norway
Scandinavia
The Baltic Sea does not border any one continent from another. It is a body of water that is surrounded by European countries.
the Scandinavian peninsula
Scandinavian peninsula
The Baltic Sea is entirely surrounded by the countries of northern Europe: Sweden, Finland, Estonia, Latvia, Lithuania, Poland, Germany, and Denmark (and the Russian exclave of Kaliningrad).
The Scandinavian Peninsula is a peninsula in Northern Europe. It includes the countries of Norway and Sweden as well as parts of Finland.
Southeast
The three Baltic republics are called the Baltic states, Baltics, Baltic nations, or Baltic countries. The countries include Lithuania, Latvia, Estonia.
The three Baltic republics are Latvia, Lithuania, and Estonia