I have a question for you: Are you really working?
When it comes to training, the mental constructs we build to guide ourselves in the gym are very important (increasingly so the longer we have trained). We as humans love numbers and patterns, and find it very easy to grasp pulling on handles and pushing on levers BUT: Are we thinking about things in the most practical and effective way?
The sets and reps are not magical numbers that somehow just work. 4×8 could be just as effective as 3×12, or 6×6, or 2×18. The loads for each of these would likely need to be altered and they would take different times to complete BUT: If each set is done with good form, at a weight where the prescribed reps leave you adequately close to failure, with enough rest between to recover, they could all be effective to some degree. If your program says 3×12@42kgs and you go through the motions barely feeling any resistance, it will probably have little effect.
The numbers are to count the work we do, not just an arbitrary prescription, so remember to ask yourself: Am I really working? If not, modify some of the variables and try again, and hey, maybe get some advice from an amazing trainer