Do you have some more information about your test? More specifically, do you know at what heart rate your anaerobic threshold is? How big a gap is between AeT and AnT?
If you divide your AeT HR by your AnT HR, and then multiply the result by 100, you’ll see what percentage of AnT is represented by AeT. If AeT is less than 90% of AnT, then you should continue to work on building up your aerobic capacity by keeping all activity below AeT (even if it’s very slow.) This applies to all activities, no matter how slow.
For example, I don’t bike very much. But when I do, my AeT on the bike is far lower than when I’m running or skiing. Even though the HR of AeT is much lower while biking, I still stick to that relatively low HR, because I want to keep things aerobic.
This can be frustrating, I know. But slowly, over enough weeks and months, you’ll find that your AeT will gradually rise. As a rough rule of thumb, once AeT is 90% or greater of AnT, then it’s time to start adding some intensity, but not before.
If you add intensity before that point, then (to quote Scott J) “you’re putting icing on a cake that isn’t fully baked”.
I hope that helps clarify things.