[Evita]

It sounds perfectly normal, don't worry about it. After a few sessions you will get better used to wearing the fin and navigating it.

It is not uncommon for competitive freedivers to wear fins that are so tight that they become painful to wear after less than an hour, but if you're just using it for training and recreational freediving, I don't see the point. It is lucky then that the footpockets are just slightly too big, because that way you have more options for how to wear it.

Maybe you should try to fold a plastic bag around each foot instead of the thicker neorene socks - the plastic bags (think thin bin liner or a large "freezing bag", 15 litres or equivalent) will give your feet more space in the footpockets compared to the socks and you can better adjust the thickness needed in each footpocket if you think the right one needs a bit more. I'm not joking, we really do use plastic bags as socks in monofin pockets, they prevent chafing too :-)