Progress in days 25 and 24 - OG Set 4

Did 60 problems in two days. Scores dropping. Must be because I'm working on 600-700 range problems now.  My scores for OG-12 set 4:

PS - 20/30 - 66% mistakes: 48, 49, 50, 56, 60, 63, 66, 67, 69, 73

DS- 20/30 - 66% - mistakes: 48, 49, 56, 61, 62, 64, 65, 70, 72, 73