That's not how you properly top a plant bro, the way you did it killed all new vertical growth, since there's no sprouts for new branches to come out of. You would have to top it again further down one more node to where those small little tiny new branches of new growth are coming out of to be able to rectify the vertical growth.
And he's right you dont have to trash them, you can fight it out and recover the plant, your going to spend at least 45-60 days vegging the plant to get a decent amount of bud out of it since you would need at least 5 to 8 viable colas. And you need to account for days in recovery from toppings. It's just a matter of wether you want to spend the time doing that.
Growing cannabis isn't complicated once you know what to do. It's more time consuming than difficult.
This has already served as a learning experience, now you know that you shouldn't feed the plants nutes in the seedling

stage, they get all their needed nutrition from the cotyledons.
Once the cotyledons die off, then you can start to implement very low doses of nutes.
Also keeping your plants directly under the light is a must, at the correct distance for each stage and the correct intensity.
You also now know that the way you topped the plant was incorrect, we can help you in your next topping.
If there's no need for you to struggle trying to correct this plant then don't, if you want to use it as an experience and see what it takes to get her back in track go for it.
I just gave you my personal opinion on the matter, everyone goes about their grows differently and I respect that, so whatever you decide to do we will all try and help you as best we can. Keep us updated.