Okay - First I completely understand how you feel about drawing things outside your current skill level and after your attempt you feel its lackluster or not to your expectations. BUT
Thats Art. If you don't try and push yourself each time you will do the same things over and over and only microscopically improve.
Theres a bunch of classes here that break down the fundamentals and you should take time with them. Use them as exercises that build real muscle. Create an Art map of your favorite artists that will give you an idea of the art YOU like to make. Also finding your niche and groove happens by accident you cant force it. Let it flow to you in time!
Sure fire way to improve. MASTER Copies, Tracing (Yes, Actual Tracing* digital and Tradational) and experiment.
When you master copy dont just copy without thinking. Analzyse why you like the art and mimic as close as possible everything you can from it. Lines, color, effects etc
Do a 1 to 1 study. Do one master copy and give yourself time to do it then do your own piece using what you learned.
Create small projects for yourself that go beyound the scope of pin up art. Find other mentors that will deversify your skill set. Join some patreons.
And give yourself a break, Its a sprint not a marathon.
Get feed back from artists underneath you, at your level and beyound you and take all of it at your discression. Non artists arent looking at things the way you are so your Dad is only going to help or hinder you.