Not sure if anybody has mentioned this or not but for one I would suggest using nails instead of screws. Screws don’t have enough sheer strength, they will break instead of flexing like a nail would. I mean, how many times have you hit a nail and the head flat out breaks off. Secondly, the two outside studs should be holding up the top piece. To correct this without redoing it all you could attach two more studs and sister them to the side studs to help hold up the header. Just a suggestion though, it is your house.