Will my accent have an effect in the TOEFL?  

Hey,

American, British, or L1 (almost close to native speaker) accents are acceptable, & can also help you to amplify scores. But, if you have MTI (mother tongue influence) in the way you pronounce words in English it will adversely affect your speaking scores of TOEFL.

Having said that, accent is not the only factor that will be considered and given you scores, instead other parameters like grammar, flow of thoughts, content, sentence structures, usage of good vocabulary and etc are also equally important.

Hope it helps 🙂