Are they stretching ?

I like to have 35 watts of good quality LED lighting per square foot (375 watts per meter2). This is about the upper limit for lighting without CO2 so it allows you adjustment room to run your light at lower power or to raise it higher. Instead of guessing at lighting levels you can download a light meter app for your phone. I like "PPFD Meter" and it is free. Then with a Daily Light Integral (DLI) chart you can see how much/bright light you need for how many hours each day. This makes it easy to use variable power lights and figure how high to hang the light.

It's WAY too high... 20W?! You're not going to be able to grow much with only 20W but hopefully you have other lights either coming or waiting to be installed? You'll need at least 100W, preferably more. But the quick answer here is that you need to get that light down to around maybe 25cm and if they continue to be leggy, pull it down even further... Good luck