First of all, get a diary going for your grow... if you have questions in the future, it will help everyone help you more accurately!
Now... to your question... you want to get this little lady into a pot with more soil... the question I have is whether this is an autoflower or a photoperiod... if it's an autoflower, put it into the pot it will finish out its life in - in other words, autoflowers do not like to be transplanted so choose the size of pot you want (I would recommend a 3-5 gallon for an auto indoors). If it's a photoperiod, you can put it into any size pot right now as they don't' mind being transplanted as they grow larger. Make sure you've got the humidity up in the 70% range and turn your lights on to veg... again, I don't know what kind of lights you're using or their strength or if they're dimmable... if they're not dimmable, turn them on but shade the seedling just a bit so it's not getting DIRECT light for a day or two. Put your lights at least 18" above the plant once it's in the pot. And finally, don't overwater and don't feed it anything right now. Again, the feeding is going to depend on whether it's an autoflower (they don't like anything for about 2 weeks other than a bit of water) or a photoperiod (they can take stronger nutes than autoflowers).
To sum up - get it in a pot and give it a little bit of ph'd water (range should be between 6.0-6.5), turn your lights on and start a diary with as much information about what it is and what you're doing and what your set up is as possible...
Good luck - and enjoy the journey!