Thank you so much for your replies! This website is a brilliant resource. I've never posted on a forum before so really great to have a response! Thankyou!
In reply to RochesterKnitter - I do have the same number of stitches from cast row to 1st row. I was adding more onto my cast on row to use up the yarn (whilst I was on my first row, rather than adding additional stitches to my first row). In terms of giving it a tug, I'm still left with quite a big loop with the slipknot maybe a cm or 2 away from the needle and I'm still not sure this is normal.
GrumpyGramma - That is interesting about the cast on. The yarn distance between the needles is increasing after every stitch I make on the first row. It just gets longer and longer.. .. to give you an idea (you might laugh here!) with the baby blanket I cast on 55. I thought it wasn't big enough so I cast on 100. I continued to my first row and with this yarn growth over the first row I ended up having to cast on another 50 to use it up!! (I did this using the thumb method I was using). It will be the most ginormous baby blanket! So anyway, it sounds like there is a problem with my cast on, and I will check out and give your recommendations a try tonight.
Salmonmac - thats great you agree - and I will check the videos out - I had gone for the easiest looking option in terms of cast on so I'll just have to learn a new one. This definitely seems to be the root of my problems
I'll give it a go tonight and let you know how I get on - thanks for your help!!