Wiring ballasts is a bit tricky, and there are several common wiring mistakes. However there are 2-3 different wiring schemes in use, so we can't walk you through it "blind" - we need pix of the ballast and what you've done.
Staying with real fluorescent is perfectly reasonable and don't be goaded into switching to LED. Fluorescent tech has advanced beautifully and 90CRI light is just normal, with no flicker or cold startup problems. LED still has major quality issues, DLC or not, and I still don't believe you can get a quality LED "tube" for $12.
Our local Target was built 4 years ago with T8 fluorescent, and they just changed all the fixtures to LED, probably for energy credits. (I wish I had been at the dumpster to snag the old gear!) What I notice now is several of the fixtures are out. That's buying commercial grade made-to-be-LED fixtures, not even retrofit tubes. Consumers cannot afford quality in LED, they easily can in fluorescent.
So get us some pix of your fluorescent wiring. There are several ways for ballasts to be wired, they are not necessarily color coded the way you might think, and there's also the possibility of a mismatch between tube and ballast. I want to look at all of those. We'll get it right! And 10 years down the road, the light will still work.
There's no way to go any further with the "how to fix it" conversation, because you have not yet provided the details.
Now if you really want LED, that is not a problem either. I quite agree you should only use ballast-bypass aka direct-wire, and with double ended LEDs, those double pins at the end of the lamp are for 18 volts not 120V. Being double ended makes the LED 25 cents more expensive, which is why cheapies are single ended. Double ended means if you plug a single-end LED or real fluorescent in it, nothing melts and explodes.