Anxiety

I’m 19 and a lifeguard. To be a lifeguard there’s a certification u need to get that requires u to swim 300 meters. I used to be able to do that but ever since I got rlly bad anxiety (mainly related to health) I’ve struggled bad. I’ve done it about 2-3 times since getting anxiety (I’m on pills) and it’s went bad. One time I was half way through the swim and couldn’t breath, panicked and just got out of the pool and cried. It’s so embarrassing. This lady wants to hire me and I have to do the 300 meter swim in order to do it and I’m so scared. I don’t wanna panic or not be able to do it cause u only have 10 mins to do it!! :( I don’t wanna do this

Edit: basically what goes through my mind is that I can’t breath properly, what if I have a heart attack? Or I panic and embarrass myself? Physically tho I am capable but my mind tells me I’m going to die or embarrass myself.