Use turns at the wall to help keep your flow and rhythm in your swim. Here is my video on how to do an open turn. I like to keep the steps simple, like almost everything I do. Use the key “duck, slap, push” to process your steps.
If you want to get a sense of your pace fore a one hundred, then having a good turn can make a difference in your pace. You may be swimming each 25 at a good clip, but your turn at the wall can be slow and inefficient such that it skues your overall time. Swimming your 100 with slow turns would not be a clear indicator of what your true pace is.
Work on your turns.