So, I'm trying to get to a low-Kerbol orbit since I have a contract asking me to get a bunch of scientific measurements from there and also because if a process all of that science in a mobile lab, I can probably upgrade everything I can on my R&D facility level. My current problem is that I run out of fuel on my last stage when my peristalsis is around 3-4 million meters. Whenever I add more fuel, I just use more getting to orbit around Kerbol since my craft is already like 500 tons. I have more then enough funds and leveled-up facilities to build things, but I started playing KSP around a month ago, so I don't know what my best options are for this.
Just to add: In all of my attempts I just burnt prograde until I was on an escape trajectory from Kerbin, then warped to my Kerbol orbit apoapsis, and when I was there, I would burn retrograde as long as I could.