The EU is not the biggest GDP continent, not by any way you would slice it.
Choose any source: The World Bank, OECD, ...
Keep those delusions handy, I'll be sure to break each time.
World Bank
http://data.worldbank.org/region/european-union?view=chart
http://www.tradingeconomics.com/european-union/gdp
EU member nations are:
Austria, Belgium, Bulgaria, Croatia, Republic of Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden and the UK.
However, with the Brexit we will be removing the UK from that list.
UK GDP = 2.86 trillion
http://atlas.media.mit.edu/en/profile/country/gbr/
EU without UK
16,311.9 - 2,860 = $ 13,451.9 billion <<< 18,036.65 billion (US)
Let's not forget that you said "continent". The US is in North America, which includes Canada.
US + Canada = 18,036.65 = 1,550.54 = $19,587.19 North America is the biggest GDP continent.
The US is bigger than the EU.