27 Days old plant stopped growing

can't be certain. is it in a small pot? that can impact how large they get. (2-3 gal should go upto 36" or more if treated well, substrate would impact that too.) did you top it recently? could stall it, just give it time. also, i cannot tell from picture but doubt this is the case -- make sure internode space is decent... if growth nodes are stacked on top of each other with no spacing, move light further away from plant... this too will prevent vertical growth at some point (too much light for ambient co2) if all these things check out and it starts to progress like a normal floering plant, then, yup... likely a dwarf.