The answer is that we can escape.
If we would start moving in the opposite direction of the goblin he has to walk Pi*R to make half a circle and we have to row R. Since the distance is Pi (3.14) times larger for the goblin but he walks 4 times faster than we can row it is easy to see that we will NOT beat him like this. We will get eaten.
So we have to be smarter and keep an eye on the goblin as we row and always move in such a way that the center of the lake is always between us. Lets assume the goblin moves clockwise and starts north. After the goblin has walked 1/4 circle he ends up east. We now have rowed in a very small half circle path starting at the center and ending west of the centre (still exactly 180 degrees away from the goblin). During this we have always been exactly 180 degrees away from the goblin.
We now have reduced the distance we have to row in a straight line to R-1/4R = 3/4R while the distance the goblin has to walk is still R*Pi.
(In the time the goblin can move 1/4 of a circle we can move half a circle of 1/8th its size, so we are the diameter of a 1/8R circle to the west which is 1/4R)
Lets assume the speed of the goblin is Vg and the speed of the boat is Vb.
We know the goblin moves 4 times our speed so that leads to: 4*Vb=Vg.
The time the goblin takes to walk half a circle is: (Pi * R)/Vg = (Pi * R)/(4Vb)
Our time to go straight to the coast opposite of the goblin is: 3/4R / Vb
So in order not to get eaten we must be there in less time so:
3/4R / Vb < (Pi * R)/(4Vb) or
3/4R < (Pi *R)/4 or
3R < (Pi*R) or
3 < Pi which is true as Pi is 3.14....
So we can make it.