2009 Civic si

I’m a new to driving manual and I switch to 3rd gear around 27 miles and I can go up to around 45 mph until it reaches around 3000 rpm when I switch to 4th the rpm’s go higher for some reason and if I switch to 4th gear when I’m around 40mph it has a higher rpm then if I were to stay in 3rd gear. I’m not sure if I’m shifting wrong or if the car has problems. I drive a 2009 civic si and it’s my first manual car so I can’t compare it to anything else.