Watercolour paper is not a neutral surface. It is an active participant in every mark you make. Cheap paper, anything wood-pulp based, anything lighter than 200gsm, will buckle when wet, cause paint to pool in the creases, and make wet on wet nearly impossible to control. This is not a problem with your technique. It is a problem with the paper, and it will improve immediately when the paper changes.
What to buy
The sensible first purchase for most people is a block of Fabriano Artistico or Arches cold-pressed at 300gsm. Blocks are gummed on all four sides, which means the paper stays flat as it dries without any stretching or taping. Cold-pressed has a light texture, visible tooth but not aggressive, which handles most painting approaches well. Hot-pressed (very smooth) and rough (heavily textured) are specialist surfaces worth exploring later, when you know what you are trying to do and why the surface matters to it.
Why cotton matters
Papers made from 100% cotton fibre handle water differently from wood-pulp papers. They absorb moisture evenly, dry without buckling at heavier weights, and are durable enough to withstand reworking, lifting, and the occasional damp sponge. The price difference is noticeable, but the working difference is significant enough that most painters who try cotton paper do not go back.
Student-grade paper has its place, for warm-up exercises, colour mixing tests, thumbnail sketches, but not as the surface where you are trying to learn what the medium can do.
If budget is a constraint
Baohong and Hahnemuhle are worth considering as mid-range alternatives that use cotton or cotton blends. They are not identical to Arches or Artistico, but they are honest papers that behave predictably. Start there, work your way through a block, and let the paper become familiar before you change it.