If you think you will go better in general, do general. Have a look at the work they've done so far, talk to the teachers,
see if you think youd be able to catch up.
2U's good scaling will only affect you if you DO WELL in the subject. If you dont do well, like under the half way mark in rankings then the rest of your cohort will drag you down and the scaling will be negative. If you do WELL in general, the 'bad scaling', will not affect you. Its better to do well in gen than bad in 2U.
Are you doing enough work at home? I know it sounds stupid, but really, just doing homework helps so much. I bought a really basic book called 'Accellerated Maths Learning' -Yr 11 2U, and just worked through everything from scratch, took time to write notes etc, just to make sure I knew all the foundations before we started the new stuff. It really helped and I went from being at the bottom to getting 95% on my last exam
Also have you heard of 'maths online'? There are lessons on there where a guy just talked you through all the topics.. I find it really helpful. I'm not a natural maths person either, but I bet if you just worked really hard, start from the bottom up you'll be sweet in 2u