Keep at it bro! Haven't had spider mites but I have fucked up plenty of plants to where I felt like stopping too but then I got a second smaller tent (2x2) so I can have 2 babies and 2 flowering in my bigger (3x3) tent. This way if something happens i always have some babies to kinda fall back on. Just keep popping seeds till you get it right. Are you taking your plants outside? Or are spider mites common in indoor grows? I've never seen em so I'm only spitballing here. Maybe try getting soil from a different source.. Amazon has been pretty good to me honestly. Couple of fungus gnats but nothing like I hear people complaining about.