I guess this would be too late for you, but one way to visualize how far some bags will go is to lay those bags out flat on top of your bed. If the bags touch all the way around, you are about to add a layer as deep as one bag is thick. (3-4"?)
I would also mix any "alleged topsoil" with organic matter and anything else available to improve its drainage (like shredded pine bark fines or grit. Perlite if it is cheap enough.
One "dirt yard" sold me top soil that seemed much more clayey when the truck dropped it, than it did in the part of the heap that they showed ME! So now I'll be suspicious and cynical for a few years.
For gardening, especially if you have a raised bed, something lighter than "topsoil" might be desirable. I think of topsoil as something suitable for starting a lawn.
And your Lowes may be different, but some places consider "topsoil" to be any heavy thing they can get away with selling, while their "potting soil" might actually be better for garden soil. Good luck finding something light enough for really using in pots, unless your HD is MUCH better than my HD!
Other people have said they can use things called "potting soil" from big box stores AS potting soil, so either they have better stores than I do, or they manage to use much heavier, water-retaining mixes in their pots than I've been able to. Maybe both!
