Practice maintaining a rhythm over poles and small fences, focus on the quality of the canter rather than arriving to the fence. Count in your head the strides coming down to a fence. Also play with the pace of your canter, the more rideability you have, the easier distances will appear. Dont stress if you don't always see a distance, focusing on a quality canter and rhythm will create distances. Good luck ☺
Always look in the fence and try to feel each stride by your seat.
Put out poles in front of the jump and count using them as an aid, then take them away and try to count the strides as if they were there