Start small to get comfortable and then grow from there. Start with a block. Then grow to two, then three, and so on.
You are nervous because u do not want to mess up a topper that took forever. 1 - 3 blocks take no time, no big loss so no worries to make u nervous.
Use lots of pins and take your time. Afterall, Rome was not built in a day.
Good luck and happy practicing