When you grow potatoes you should bank up the soil around them when the shoots are about 2" high. Each time they grow 2" bank up again until you have done this a number of times then leave them to flower. After the flowers have died off the leaves and stems will eventually start to wither and die back. After they have died back a bit do a bit of exploring with your fingers to see if you can feel how big the pots' seem to be. If they feel big enough for you just dig one plant up to check. If most are still small leave the rest for a few more weeks and do it again.
Some people seem to be able to plant the seedlings, leave them without too much attention and get great crops, others don't seem to be very successful no matter what they do.
Don't get disheartened. Gardening is an art that needs patience and acceptance that some things will fail. Next year they may not.