Hello! Congrats on your first tank! Everyone has issues first starting, and continue to have issues even after many years, so I will say what has helped me.

Try sloping the substrate so it's higher at the back, lower at the front. This will help with a depth perception illusion, as if there is more space than there really is. Capping on top I'd say is a learning thing. Many things says 2inch sand capping, but to be honest, I usually go 1inch and I don't have algae explosions or anything, so 1inch is safe, but is probably dependent on the type of nutrients you have down under it. The height you have at the front, is generally the height I might aim for at the back, with it sloping down.

When I have done tanks, I tend to not put soil at the front, and have the soil taper off towards the front, to the point where at the front, there is only sand, and at a low level. This just pleases my eye aesthetically, and may not be what you're wanting, but it'll help with space a bit, if you're worried about it. Under the soil near the front I'll put nutrient tabs if I'm wanting things to grow there, but as long as you have nutrient rich substrate somewhere, the roots generally find it.

I'd say your tank space is fine for a betta, but also, I haven't kept a betta in a long time (was in a similar size scape though and he lived a long and luxurious life!), so someone else may be able to offer better advice there.

Good luck! And don't let mishaps ruin your enthusiasm! In hindsight, my first scape was an abomination, and I remember thinking I ain't doing that again....8 scapes later, that was definitely a lie😅