I tried it for the first time this week too and couldn't keep the pace either...it being in a hot stuffy room overlooking a nice cool swimming pool definitely had something to do with it. The class is like musical statues or something, people get too tired, stop and walk (or crawl!) out the class so by the end of the hour there's less than half the number of people it started with!
I'm from Hull....it's safe enough in an organised event but a bit of a no-go area if you were to go for a recreational run on your own with ipods and fancy watches and things. Lots of unsavoury people about (to put it politely)! As soon as you get out of the city centre it’s ok. But after this year's marathon there was a lot of complaining about the course not being measured properly, lack of race markers, few organisers etc. Better places and events to run in to be honest.
I used the couch to 5k to get into running for the same reasons as you...I remember the first 3 weeks were tough but after that and it doesn't seem like as much a jump in difficulty each week. It also gets a lot easier and more enjoyable with less stopping and starting
If youre combining it with other exercise on weekends it shouldnt be long at all until you see and feel the results! Give it maybe a month, less if your eating healthily. July is plenty of time to train up for your race, and if you stick to the 5k plan you'll easily be able to run the whole thing!