Tracey, don't be downhearted - tbh, a training class environment is the most difficult place to train a dog
All the good training books I have (especially the Complete Idiots Guide to Positive Dog Training by Pamela Dennison) advice that to start teaching any behaviour, you chose a low distraction environment that the dog is familiar with. Once they have learnt the behaviour in that environment, you move it to a different place, with the same level of distraction, and start again
Once they have "got it" in several low distraction environments, then you can "take it on the road" and begin to introduce distractions........imo, a training class, in a paddock, is right at the end of that journey...and certainly not achievable within a week
Stick with it - take her training sessions out with you, so you practice in different locations and environments, and slowly, you should begin to notice that Ruby begins to pay attention to you.....but there may always be the odd time that you lose her
At this weeks agility class, Molo found something irresistible in the grass and kept going back to it, he was driving me MAD - it turned out to be a family of baby frogs; and no amount of garlic sausage or liver cake could compete with that