I agree with using a guide of some sort... I use a combination of vertical "templates" under the paper with a light box and also lightly sketching my letters in pencil (especially when I do Cadels.) Light boxes are not that hard to make, if you have anyone that has a basic wood shop... or they can be ordered on line as well. I love mine (my dad made it years ago.)

That being said, I think you are being too hard on yourself. Your work is lovely and everyone's hand is a bit different. Just keep practicing and you will notice an improvment over time... but I really think this is lovely.