Perhaps this is your scenario.
Did you run source devel/setup.bash
on the same terminal where you are attempting to run your package? After (re)compiling your package, you need to source devel/setup.bash
on each terminal, otherwise they will not know about your changes.
Additionally, since it appears that you modified your package a number of times, you might need to remove build and devel folder every time you are recompiling (after every change):
cd ~/catkin_ws
rm -rf build/ devel/
catkin_make
source devel/setup.bash # run this line only on the other terminals too