is maths alevel crazy hard

I'm picking my A-Levels right now and I'm thinking of picking Maths as my fourth except my maths teacher begged me to not pick it (not the most optimistic guy ever) and went on a whole tangent about how I'll fail from day 1. I got an 8 on my mocks without incessant revision so I don't think I'm horrible at it but i keep hearing about how it's a lot harder. i'm definitely willing to put a lot more work into maths next year but i just really want to know if its actually as hard as my teacher's making it out to be. should i pick it?