I reckon all the above is good advice. When my missus did her CBT, she also found it hard to get much above 30, and the instructor advised her to go and ride around on a 125 for a while, to build her confidence up. My guess is that, if they feel someone's going to need a bit of time to do this, then they advise this as it's going to work out cheaper than continuing with lessons. But it's up to you; whichever way you choose, you'll continue to learn. Even if you can get a 125, then you might want try doing something like one lesson every month or two, so you continue to get some instruction as you go.