Do I have to be good at Maths to achieve good results in IB Economics?

The answer is a definite NO. In the IB course, the focus is really on the basic understanding of different economic theories and how they are applicable in the real world. Only if you take Economics HL would you need to face a paper with numbers. Paper 3 would examine some mathematics based on the economic theories and their equations you have learnt, but they don't contain complexed operations and the paper is 60% math and 40% written work.