You might need to take that swim time with a grain of salt since open water swims, especially with triathlons can be all over the place in terms of actual distance - - it could be accurate or it could have been short (or long… Hopefully long 
). Anyway, you could look into adding some swim band training to help add some extra time to your week. I’ve done that in the past when I haven’t really swam over the winter and while it’s not a perfect replacement (obviously), it does help. I just use a resistance band set looped through a door jam attachment. It really allows you to focus on the catch. Just make sure it’s a light resistance band so you can get some nice stretch out of it (actual swim bands may be better, but I’ve never tried them). I count strokes for the sets, so groups of 50s, 100s and even up to 200 sometimes and go for 30-60 minutes depending on time available. It’s not much less boring than staring at the black line, and you can have music 
.