Ender 3 X axis not level
i've just bought an Ender 3 Pro and on assembly I carefully checked and deburred the uprigh rails on their bottom faces to ensure they did not splay out or in etc.

Once the 2 uprights are loosely attached to the base rails I laid the assembly flat onto a table on the uprights to ensure the uprights were square to one another and tightened the screws.

Check the uprights are parallel to one another by placing the top crossbeam on the top of the uprights and check if the screw holes are alligned...….if the screws are tight to enter their holes the uprights are splayed out or in and need correcting etc......a small amount of pressure "can" make them line up. 

The X axis rail slides up and down on the two uprights with two 3 wheeled brackets, one either side, that have 3 wheels on them, one wheel on each bracket is the adjuster and it is easy to have the X axis cross beam out of square if you tighten the one bracket to the rail before you test the rail for squareness.

Firstly, place only the 2 wheel brackets on their uprights and adjust the wheels for smooth running, then attach the X axis rail to each wheel bracket and just nip up the 2 screws loosely to hold them to the cross beam.

Now, check the cross beam for squareness by running it to the top of the uprights and measuring the gap left to right between the X axis rail and the top rail, then tighten the left hand wheel bracket screws to the X axis rail......and then tighten the right hand wheel bracket to the cross beam.

Leave the Z axis leadscrew off for the moment and run the crossbeam up and down on the uprights making sure there are no tight spots due to out of squareness.

if it's all freely moving.....fit the Z axis leadscrew.

The bed plate can only be set once you have the machine itself squared up.
Ian.