I have a shower pan that is not level all the way around. It is level on the two ends ,or the short walls, and then slopes all the way across down to the drain. It seems to me that this will let water ride along the curb and the back wall. Is this correct? How do I fix this if the tile is off and I am looking down on top of the finished thick mud bed. The liner is already in and mud on top of that?

So two sides of the shower are lower than the other two? Can you use a short level and determine if water will drain from all four walls toward the drain? If it doesn't, how low are the low spots? There should be 1/4" of slope toward the drain for each running foot of floor.

Yes all four sides have slope to the drain. The long sides have a little dip in them sloping to the drain. Across the short sides it slopes directly to the drain. It has the 1/4" slope all around.

If it's all sloping to the drain, then your ok. The only issue is having to custom cut all the wall tile on the bottom rows where the dip is. Not a big deal if your patient.

I would level up the perimeter with thinset and skim part of the floor area to make up the differences.

The dip is 6" wide sloping toward the drain. The tile is 3"x3".

Maybe you could post a photo that has a straight edge laying across the problem area.

How thick can I apply thinset without it cracking? I assume this is without lath. RC I will try to get a photo up for you to view. Thanks you guys for your expertise.

Some thinsets can be used as leveling layers up to 3/4"
Look for a thinset specification that says "medium bed"

Unfortunately,I don't know whats sold in your area so I can't give you any specific brand names.