Let me know if none this fixes it:
First, make sure your Minecraft username (aka Minecraft account name) is set correctly. To do that, go to the Account (gear) tab in the middle of the LearnToMod homepage. Then check that your Minecraft username matches what you see on your Minecraft launcher exactly - it is case-sensitive. It most likely shouldn't be an email.
Confusingly, the username that appears on the Minecraft launcher play screen (the screen you see after logging in), will be in all caps. Eg: Suppose my in game username is Modder. The Minecraft launcher play screen will say MODDER. But if I click MODDER, from the drop down menu select switch account, and then scroll down down, I'll see it correctly capitalized as Modder which is also how it should be capitalized on the LearnToMod website.
Now, go back to the LearnToMod website. You should still be on the Account (gear) page..
If your username ISN'T set correctly, click the blue 'change' link then type the correct Minecraft username.
If it IS set correctly then try using the command square on the server admin page to run op YourMinecraftUsername
Or try typing /op YourMinecraftUsername into the chat area in Minecraft after entering your world.
Just replace YourMinecraftUsername with the real Minecraft username.