1. It seems really small for a 4week old
2.The stem seems fine to me
3. the cup seems the right size for a few weeks if thats how slow your plant is, but i think you should give it more room as soon as it starts getting significatly bigger
I had one 21w 1600 lumen light for the first month and then bought an other. it seems to do pretty well, but it's SLOW. I don't think you'll be able to rush it to 2 months.
I suggest you read the "Cannabis grow bible" by Greg Green. When I started growing I had a ton of problems with it first but Gregs book had a load of useful tips :). I'm a newb growing inside so I can't really help you, but I know the CGB has a lot of info on growing outside! :D