Maybe your arms are weaker than normal, which is why you feel it more in your arms. If you practise the shoulder and arm strength exercises alongside this, you will see improvement, and will start feeling more in your core.
There are always modifications suggested in all the core exercises. Please practise the modifications, and stop at the simpler versions until you get stronger.
Even just holding in quadruped for 20 secs, and repeating the exercise, will help build your core.
My suggestion is to build your arms and try the quadruped exercises, from the first legs and core, in the strength series. These exercises are the simplest versions, so stick to that for a while and dont hesitate to stop inbetween and pause as well. This video also has the toe tap while lying on your back. So do that slowly and with awareness.
The later exercise videos in the series get harder, so dont do the core strength videos that have ben introduced later, until you are comfortable in quadruped.
Hope this clarifies.