Trying an unknown strain.

I recentley decided to plant Marijuana for my own consumption. One of the reasons i decided to plant my own Marijuana was because here where I live you don't find any place in a radius of 100km where they sell buds. Nope all you get is the scraps of to early harvested miniature buds with a mix of leaves, seeds, sticks and even sometimes little rocks in your baggie. Also there is no place for me to purchase seeds of any kind so I just took some from one of the baggies which had the best taste/effect. The Plants are now one and a half months old and about 17 cm long. Do you think my harvest wil be good or bad because i didn't buy a strain from a seed bank?

it will be hard to tell what you've got without some pictures, from your description the plant sounds small for its age
but it's quite possible to get excellent results from bagseed, often the genetics are good, good chance it will be better than the bagweed

if it's a lady, and you treat her good, you'll be fine read a few of uncle ben's pointers and you wont go far wrong https://www.rollitup.org/advanced-marijuana-cultivation/267989-uncle-bens-gardening-tweeks-pointers.html