Over time hydraulics can seep slightly and the motor move down, but not within a few of days.
It could be as simple as the tilt screw being loose or defective or something inside the trim unit. Sometimes running the motor all the way up and hold the button down for a few seconds, then do the same all the down helps. Also loosen the manual release screw slightly and hold the up and down button for a few seconds each. If it is a microscopic piece of debris, that may flush it away.
If your motor is still in warranty, ask the dealer to contact Evinrude dealer support for assistance.
"There is never just one thing wrong with a boat";
-- Travis McGee, main character in a book series by John D. McDonald
The factory recommends that a properly trained technician service your Johnson or Evinrude outboard motor. Should you elect to perform repairs yourself, use caution, common sense, and observe safety procedures in the vicinity of flammable liquids, around moving parts, near high-temperature components, and working with electrical or ignition systems.
The information offered here is only general in nature and should not be construed as complete factory approved procedures, techniques, or specifications. Always use the proper service manual for your motor, up-to-date service literature, the correct tools, and have an understanding of how to proceed with troubleshooting and repair methods. If you are unsure or uncomfortable with a procedure, a situation, or a technique, enlist the services of a factory trained technician.