First make sure the container is lifted from the floor to give it a good chance of draining properly. If its a reasonably small container you can sometimes tip it carefully on one side and let some of the surplus water drain away, if you can manage without the compost coming out as well. Put it somewhere where it wont get rained on until its dried out - somewhere sunny with good air circulation will be best. Plants die of overwatering because the roots drown. but this doesn't happen overnight, so your beetroot will probably be ok. And remember more pot plants are killed by overwatering than underwatering.