The first thing I've got to say is well done! Any exercise, whatever you can manage, is good for you and will help your health.
Many people find their bg levels can go up if they exercise, this is a response to the stress and elevated heart rate, causing the liver to dump reserve glucose into your system as a response, which you're unable to quickly use.
The good news is that as you get fitter this will happen less often and less severely as your body is more able to deal with the effort you're requiring of it. It's worth keeping going. If you have problems with high bg, maybe don't push yourself as hard as quickly, gently step up over time. Of course, you may have no problem! See how it goes. Good luck!