Chapters do screen heavily for psykic potential yes. But it doesn't always manifest immediately after implantation of the geneseed. Sometimes it takes years or decades. 

Your powers would likely be minor. Little things happening around you that you can't explain. Things that seem to help you when you need it most. Or you have an uncanny knack for prediction.

If you immediately showed as much psykic power as you seem to want to have, you wouldn't be hanging out with the other scout marines. The librarium would take you away for their own training. Because having you roam around with untrained and refined psykic powers is super dangerous.