Personally I always shoot for getting 5 Catfish on day 3. If I get more, great! I rarely get less. On day 2 I'll get to at least 4 fishing skill (fishing in either the ocean or the mountain lake depending on my mood, both work), and get at least 1800 gold (typically much more). On day 3 then I'll buy a Fiberglass Rod, plus bait, and if I'm only at fishing level 4 still I'll grab a trout soup or two, as catching catfish at below 5 fishing is quite difficult.
One thing I've heard people do (but have never done myself) is buy a training rod day 2, and use that to increase their perfect catch rate. I'll readily admit I miss a few perfect catches on that 1st day, so I could probably make it to fishing level 5 more consistently if I took advantage of that, you might find it's beneficial as well.
Note that catching those catfish consistently or not matters quite a bit, not only to the amount of money you're earning on those days, but also to the amount of fishing XP gained. Each cast which reels in a catfish earns you at minimum 28 XP, each cast where one got away earns you 0 XP. If you can't catch them relatively consistently (at least 50% of the time), you're better off not fishing in the river, as each of those casts where they get away may as well be trash, and then even the relatively less valuable fish in the mountain lake are better options.
Hope some of that helps! Fishing is undoubtedly the best source of early income without reliance on RNG manipulation so I don't think your course of action needs major revisions or anything, I'd just practice that low skill fishing some more and you'll be fine.