Problem leveling bed on Geeetech A10

[paradeben]

Hi,

I'm new to 3D printing and kind of struggling with it, as the first layer won't stick to the bed. I'm trying different settings (see below), but I think the problem it that the bed is "wavy" on the Y axis: when I move the bed from front to back, the distance between the bed and the nozzle varies. It's paper thin at each end and at about 1/3 and 2/3, but it between it increases by 1-2mm.

I understand it could be a problem with uneven wheels. If that's the case, how can I fix it? Otherwise, what else could it be?

Settings I've tried so far:

Layer height: 0.1, 0.15, 0.2

Initial layer height: 0.3, 0.14, 0.18

Build plate adhesion: none, brim, raft

Enable retraction: off and on

Everything else is default settings (print temp 200°C, bed temp 60°C, print speed 60 mm/s, initial layer speed 30 mm/s.

Let me know if there's any relevant settings or details I should share.

Thanks.