Congrats on passing your test! Don't worry, things do become easier with practice!
As the others said, the blind spot check is a must, but it is just a flick into the area you can't see to check for people sat there (in cars) or things like R1 or other bikes slamming up your offside (there's a reason bikers call these over-the-shoulder glances "life-savers").
As for changing lanes to the right, if it helps, the way I do it is to see if the lane is clear, if not I start to slow and, unless I'm going significantly faster, I'll let the other vehicles pass then slot into a space, briskly picking my speed up to match. If the gaps are big enough, both in my lane and in the target lane I'll match speeds with the flow and slide out. For moving to the left it's a similar thing but the difficulty, especially at first will be judging the speed.
I think the best thing would be practice, even if it means judging speeds and gaps when you don't plan on moving out.
Or go on further training such as the pass plus/get a drive with an advanced driver.
HtH, MtMtMn