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You want the 52" liner. The manufacturer makes it smaller than the actual pool measurements because it's supposed to stretch into the pool. If they didn't, all liner pools would be full of wrinkles. If you went with the 48", you'd probably rip the receiving track off of the wall before the water level reached the return.

It sounds like you've got a "J-Hook" style bead, double check and make sure you get the right bead for your receiver (there are 4 different types that I know of and the bead must be the right type for the receiver you have). The manufacturer takes into consideration the receiver offset.

If you want to discuss this more, or bounce what you're planning off me, I'm here almost every night and will gladly share my knowledge and experience with you.