is this the right way to use the Present Continuous here?: jij bent de deur aan het opendoen
The [separable] verb in this sentence is „opendoen". The English verb "to open" is „openen" in Dutch, and the word "open" is an adjective in both languages.
A bit like the stressed English form "I DO open the door!" "I DO think he is mad!" Or an older verbal construction "I do off (doff) my hat". Or in habitual aspect in Irish English "He does be doing that every weekend".