The word "that" is not necessary in English sentences like this. Indeed, that fact has been recognized by Duo in other exercises Also, Duo has omitted "что" in many Russian sentences where I would have expected to see it.
The sentences are geting too complex for me to construct. it takes too much time, and it is a waste of time to sit here constructing wrong phrases and sentences. So i have started just typing something to get the correct sentence.. time to try another method.
The sentence length is adequate at this level of learning. You might be progressing the tree too fast. Consider going back and repeating lessons event though the next steps are already available. When you arrive here next time you may find this exercise to be easier.