Felix went to the witch's house without the boxes. Yes, he was supposed to bring them to the witch… But! Couldn't the witch at least help him out by casting a spell that would shrink the boxes or something? So that Felix could bring them all in one go, without running back and forth with the wheelbarrow? It shouldn't be too much to ask, right?
Besides! It was the witch's fault in the first place. He could have had all the boxes delivered to his door by Kade. Sure, he may not have known that Kade would bring double the amount of each requested ingredient… But even if he hadn't, it would still be a lot! If the witch wanted Felix to be the one to receive the ingredients so much, why couldn't he at least ask him to do it in the witch's house? Then Felix wouldn't have a problem with transporting them now… The witch knew he didn't have a car!