PPP / currency evaluation
Your conclusion is correct here. Since at the current FX rate you can buy the burger cheaply at an equivalent rate of 2 EUR in the US. So basically, if you live in Germany and want to buy a Big Mac, you are better of buying the Big Mac from the US since via the FX rate you will still have 1 EUR left(if you started with 3 EUR) and hence this will increase the demand of the USD in the foreign exchange market and hence

USD should appreciate in the future => USD in undervalued => EUR is overvalued.