New pool liner too tight?

Hello,

My new pool liner for my 12 X 24' pool was installed last week. I have some concerns the liner is too tight in the corners, all four look like this.

http://postimg.org/image/54ekur989/2857a20e/

Spongy, stretched and tight. I received the following reply from the pool company (they are looking for final payment)

The weight of the water and we need good hot sunny days and the liner will settle into place, it takes time it will not happen over night. We stand behind our work and if there is any issues, and we are confident there should not be any it will be taken care of. Again, we have not had a good stretch of hot days to help the liner settle. When the liner is put into the pool a powerful vacuum is used to stretch and put the liner into place, if there was an issue with the liner it would have been noticeable and would not of been able to be put into the pool, you just have to be patient.

What do you guys think? I'm concerned I am going to get the short end of the stick.

Jeff