Oooh im glad it's not just me having trouble, im exactly the same i have 4 cuc plants' i've had 1 cuc off one plant about 1 week ago and the rest are the size of paper clips. I've actually gone out today and put a poly over them (they are supposed to be an outdoor variety because i thought it was too cold perhaps)
I'm happy to report I cut one big cuke about a week ago and I've got one that's just about big enough to cut, and a couple more about halfway big enough. And in fact I think I let the first one grow a bit too big before cutting, because it was just starting to go a bit hollow in the middle. I think they were just a bit slow starting. I did start giving them tomato feed once a week, so maybe that's what did the trick. but now they've started I have a suspicion I'm going to be drowning in cucumbers in a few weeks. Maybe 6 plants was a few too many
One thing I have noticed is the ones I put in grobags are doing way better than the ones I put in pots. They were smaller seedlings yet they've caught up and overtaken the ones in pots. And they are very big pots, so it's not that they don't have enough room. I'd say they've got far more compost than the ones in grobags, so I don't know why.
And slightly off track here, but what's the difference between a cucumber and a gherkin? I mean, I quite like gherkins on my burgers, so if I do end up with a glut of little cucumbers would they be suitable for making pickled gherkin with, or do they have to be a gherkin variety?