From what you describe your enlarger is out of alignment. I am not familiar with your particular brand and model of enlarger but most every enlarger needs to be aligned at one time or the other. The process involves aligning the easel/baseboard with the enlarging lens and with the negative stage (front to back and side to side). There are devices mfg and sold that enable one to determine the adjustments needed. However, one can use a level among other homemade devices to accomplish this as well. From what you indicate the lens/negative stage are tilted sideways in orientation to the baseboard/easel. There may be other adjustments required as well but the side tilt seems to be your primary noticeable problem. Good luck.