I mixed up my GCSE grades on application and uni is asking for evidence

Hi so basically when applying to uni, I kind of had to guess which grades I got for english lit and lang GCSE (silly i know) because I forgot and couldnt find my certificates, however i was fairly confident that i would remember them.

Well today I found the certificate and realised that i mixed up the grades so basically I have put down my english lit grade as my english lang grade. Coincidentally, I just got asked to go for an interview at the uni, and they are asking me to send evidence of english lang GCSE. What should i do, and will this affect my opportunity for an interview? Im panicking because I actually got a lower grade than what I have put down (4 in lang and 5 in lit - I put it down the opposite way on my application), and I dont really want my own stupidity to ruin my chances.