Hi, thanks for the responses. I don't think they're apple or dahlias.
Although the leaves are serrated, they have quite rounded edges teeth,
unlike apple and dahlias.
If it helps, the leaves have pronounced veins near the base of the
leaf, and subtler ones further up, which I don't think is that common
in plants. The leaves are covered in fine hairs, though you can't see
in the pics but they are quite fuzzy.
I got the seeds in one of those dodgy "educational" sets, where you're
giving a plant, some compost and a small pot. They were labelled as
catnip, though they're definitely not lol