If you're new to MyDMX and new to the scan library editor, it can be confusing. You can set ranges to specific functions, so it's not impossible, it's just more work and harder to figure out. It also doesn't help that MyDMX will not dynamically update the profile attributes associated with the profile to the fixture. So, it's "tweak, re-load, test, repeat"
It appears that Channel 1, if you set it to 255, and the set channesl 2,3,4 to 255, you SHOULD get ALL white(RGB mixing). You don't need a profile to do this. Assign your fixture to DMX address 1, then just plug things in, launch MyDMX and move faders.
Keep in mind profiles make it easier for us to understand, but also lets the computer do things that would be more difficult for us to do individually(or at least more time consuming). At the same time, a DMX value is a DMX value and you've got 512 faders you can move.
Again: you DO NOT have to have a profile loaded to make MyDMX function. You move a fader, it sends DMX values. Plain and simple.
See if this works before you really proceed.