Is your laptop the Acer Spin 5 for sure?
Did you follow the guide closely?
[guide|127394|Replace Acer Spin 5 battery|new_window=true]
Can you see the seam when you look very closely at the laptop?
Try to widen the crack a liitle and if you don't have the ifixit tool then jam an old credit card or like plastic card into the small gap. Run it around the seam openning it as you go. That should do it.