"when I try it with both eyes open I can focus on the sights but the target is more than blurry"
It's well established that shooting with both eyes open and concentrating on the sight picture with the correct eye is best, expecially for long shooting sessions. We all develop habits early and most are bad, aiming squint-eyed is one. But, like all other habits, it can be changed. It takes mental discipline, concentration and practice. Same as grip, trigger squeeze, maintaining target fixation during recovery, etc.