Sweet Sultans from seed - weak stems

Hi, I was wondering if anyone could help - I am growing sweet sultans from seed but the stems seem quite curved and weak rather than strong and upright - is this normal? I’m wondering is it something to do with maybe over watering them as I haven’t been sure how much to water during this recent UK heatwave! Or maybe I haven’t buried them deep enough and this is actually the root? Sorry I’m new to gardening so any help much appreciated!

many thanks