Question about roots

So im told that my little seedling with only 4 small leafs is not growing out because its in a big pot,so the roots r growing rihgt now, but is it gonna make a diif when the plant grows??? will it shoot up fast 1 week, or is growing the roots out a waste of time when the plant is so small???? thanks

Its gonna be okay.
Plants need big strong healthy root systems, to grow into big fat healthy bud producing marijuana.

i have them in 3 gal pots, that should be good to veg about 2 feet, and flower after in the same pot??,

Don't sweat it.
The plant will grow.
If the roots are growing, untill a bit cramped then the plant. Then you xplant it and it starts all over, who cares? Its going to take roughly the same amount of time overall. It will just seem *forever*

Take a typical house spider plant. Once the roots get bound up, thats when it sends off the little shooters looking for a new place to root.

I've also read that a 3 gallon pot should be good for a 3 foot plant (one gal per foot) Some here don't go above 3 gal. pots