The issue in these cases is that you have a hard time not focusing on them. These intrusive thoughts come all the time, take up mental energy and time. It would be best to just focus on actually building things, but it's not always as simple.

It may alleviate the thoughts if you knew for sure that you are not an impostor from a source you can trust or perhaps it will require therapy. Or maybe you can actually push through it, as you said. Anxiety, depression and low self esteem however can take a strong enough toll that simply pushing through and dealing with it may be too difficult without help.