Hey LuckyLolek, honestly, don't overthink it!
At 36 days, 17-18 cm sounds a bit on the shorter side, but that really depends on the strain and how much light she's getting. If she looks healthy and the leaf color is good, you're doing fine. Some plants just stay squat and bushy before they really stretch.
Without seeing a photo of the plant itself, it’s hard to be 100% sure, but as long as you don't see any weird spots or drooping, just keep doing what you're doing. Every grow is a learning curve anyway!
Just keep an eye on the nodes—if they are tight, she’s just building a solid foundation. You're doing good!
**Happy Growing Growmie 🌱**