Hi Sherlly
Thank you for posting in the community! Unfortunately there is no way to add an activity between two steps. This is a good idea so could you fill out this feature request form.
There is a fast way to select your other 60 activities to create room for the new activity. Left click on the editor and hold it dragging your mouse across the items you would like to move. If there is anything in the way that you do not want to select then Ctrl + click that item to deselect. You can then move your selected items to create room for the new activity.
If I've misunderstood what you're trying to do please let me know and send a screenshot of the problem you are running into! Hope this helps!
Great!! this will help!! I will also fill in a feature request form.