I'm sure other people have run into this same issue, but given the tutorial you used it's tough to say. Running 'make install' will copy the built libraries to wherever the install directory was set during the cmake call (probably /usr/local/lib), and if the OpenCV 2.4.11 libraries were already there then running 'make install' with OpenCV3 would have overwritten in them, in which case you no longer have OpenCV2.4.11.
If that is the case (and it may not be), then you'd have to reinstall OpenCV 2.4.11. If you do have to reinstall it, you should specify the install directory as something distinct (/opt/opencv2 or something, just to make it clear that it's separate from OpenCV3).
So I guess the first thing to do would be to check which version gets picked up by your compiler by default, i.e if you don't specify any link or include directories and run a program that prints out the OpenCV version, check whether it's 2 or 3.
