There is no such thing as a dud unless you count a dead seed. This one has sprouted & while it looks small for 3 weeks old it's certainly not a dud. There is a reason for the slow growth: it could be just poor drainage which starves the roots of O2 or a related issue. Check to be sure there are drainage holes in the bottom of your container and/or drill some more if needed. Seeing you have given them only water is very good; this won't need nutrients for awhile but overwatering can slow down growth. Try watering with a hand mister to keep the soil moist but not wet and then only soak the roots with a watercan maybe once a week if at all. Also if you do not plan on using nutes be sure your source of water is chlorine or flouride free; tap water can kill the microbes in he soil that feed your plant naturally. Once they die off you will need to use nutes unless you've got enough grow space to transplant into a bigass pot of fresh mix.
Either way it would be a net loss to throw it out when you can easily recover this plant & get a harvest from it in time. No plant on earth can do a full cycle in 7 weeks; just not possible. Put any estimated finishing time right out the window & focus on keeping her healthy the entire grow. Autos finish when they want to; I hate them personally but I've run them with success. You should be on a 20/4 light schedule to maximize the small amount of veg time you've got left. Autos will flower out once they are mature enough for sex but they won't trigger until they have some height.
