There are actually two types of thornless boysenberries.  One group is really thornless and the other  are nearly thornless but sold as thornless. I suspect you bought the second type. The good news is as the canes mature they may become more smooth. No boysenberry is truly thornless despite what the tag may claim. The good news is that the new growth in spring has the most thorns and then you will see less prickles. Enjoy your summer berries and Keep Growing, Marianne Binetti