There's no such thing as a waste of time when it comes to beginners growing. Everything you do right now is a learning experience if this is your first grow, especially an outdoor grow.

Concerning your yield, it's hard to say since it was bagseed so you may be unsure of the strain that you're growing. Some strains will flower earlier than exactly 12/12, so you may not vegetate as long... but with some TLC from you, I'll bet that if you get a couple of females, and growing in that kind of soil, you may get a lower yield due to the late grow, but hopefully a nice, potent smoke if the strain allows.

And think of it this way... next year come April or May you'll know exactly where to start your grow!

Good luck, wish I could be of more help.