Sounds like you’re very hard on yourself. Young children can be very hard work and very demanding. It will get easier as she gets older and you can negotiate and discuss things more with her.
Try to keep in mind that you’re doing the very best you can for your daughter, so when she has a tantrum you can remain calm.
Losing your rag too is a vicious circle as it feeds your child’s traits. They will copy what they see, so if you can remain calm whilst she’s having a meltdown, it will help in time hugely.
Also, try to be strong when disciplining and don’t give in to her demands as by doing so you’re just making a rod for your own back.
Children need to know where the line is, it makes them better behaved because they feel secure and safe. Children without boundaries are the one’s who end up poorly behaved as they are unsure where the line is.