USPRT Workouts?

I've just found that my failure count fluctuates a lot depending on if the day is good or not. My current "standard" set is to attempt 40 x 50 m interval starting on 74", making 54" for each one. My previous best was failing on 20th, 23rd and 25th. Last Friday was a good day for me. I did a squad training session in the morning and already reduced my base pace to 1:58 / 100 m, and still feeling strong at the very end that the coach told me to try 1:56 the next time. In the evening the same day I did USRPT and pushed to 18th, 21st and 26th for the failures. I did open water swimming on Saturday and rested on Sunday, however I was feeling extremely bad on Monday. I attempted the same USRPT set and failed on the 7th, then a consecutive failure on the 9th ended my set. I didn't even make 10 intervals while I was doing up to 18 before failure on the last week! I'm now worried that how can I make sure that I feel "good" on my race day.

I've just found that my failure count fluctuates a lot depending on if the day is good or not. My current "standard" set is to attempt 40 x 50 m interval starting on 74", making 54" for each one. My previous best was failing on 20th, 23rd and 25th. Last Friday was a good day for me. I did a squad training session in the morning and already reduced my base pace to 1:58 / 100 m, and still feeling strong at the very end that the coach told me to try 1:56 the next time. In the evening the same day I did USRPT and pushed to 18th, 21st and 26th for the failures. I did open water swimming on Saturday and rested on Sunday, however I was feeling extremely bad on Monday. I attempted the same USRPT set and failed on the 7th, then a consecutive failure on the 9th ended my set. I didn't even make 10 intervals while I was doing up to 18 before failure on the last week! I'm now worried that how can I make sure that I feel "good" on my race day.