If you don't pass the test, the number of retakes that you have to do will increase day by day.
ご質問ありがとうございます。
"If you don't pass the test,"=「テストに合格しなければ、」
"the number of retakes that you have to do"=「再テストを取らなければいけない数が、」
(又は、"the number of times that you have to redo the test"とも言えます)
"will increase day by day."=「日に日に増えて行くよ。」
ご参考までに。