Are there ways in which you can overdo your thickening?
No, you can do something to underthicken it (make a darker roux than the recipe intended by accidentally heating for too long), and you can get lumps in it, but there is no common mistake(1) which can cause too thick a sauce. 

From your description, it seems like you simply used way too much flour. 120 g to the cup is a pretty common conversion factor for flour (as always with volume-to-weight conversion, it's not perfect, but good enough). 1/4 cup of flour would be 30 gram, not 60. 

Also, this recipe seems flawed in suggesting a 1:1 ratio for the roux to weight instead by volume. You probably needed 30 g flour and 30 g butter, not 30 flour and 60 butter. Sometimes it is common to overbutter roux, but not by such a margin, and the additional fat is more commonly added later, not during making. The 1:1 volume ratio suggests the recipe maker didn't know what they were doing, so I wouldn't be surprised at the recipe as a whole being suboptimal. 



(1) Before people start correcting me: Technically, there are ways to overthicken. For example, you could cook out most of the liquid, but you'd need to forget it on the stove for an hour or two, and if that happened, you'd probably would be complaining of burnt sauce instead of thick sauce. Also, if you somehow managed to add another thickener without noticing, such as throwing in a pinch of xanthan insted of pinch of salt - you see we're dealing with extremely improbable scenarios here.