[ultimaker 3 not printing correct size]

so i should change the standard settings for the ultimaker pla ?  and it is accurate but not the same as the file. if iprint the part multiple times it is always the same in dimensions it is just not the correct dimension

[ultimaker 3 not printing correct size]

6 months ago i printed a calibration cube that is 20x 20x20 and it was exactly 20x20x20. when i print it now it is 20,3 in the x 20,1 in the y and 20 in the Z i printed the cube multiple times with the exact same results so that should rule out backlash from the belts. just for good measure i re tightened  the short belts but with no change. does anybody know why 

[ultimaker 3 timelapse]

so i just bought an ultimaker 3 extended and its printing great. because the ultimaker has a camera i thought it would be cool to do a time lapse. so i opened cura sliced a print and added in the time lapse with the post processing. it worked but it had a slight issue. it was extruding filament on the way back after it had made a picture. does anybody have any idea how to fix this or do i need to change the g code a bit. your help is appreciated