Which course should I pursue after B.Tech ECE?

If you are interested in higher studies or research then you may go for M.Tech. For doing M.Tech, you should have at least 55 % in B.Tech/BE and a valid score of GATE. I am enlisting a few good colleges for M.Tech IIT Roorkee, IIT Guwahati, DTU, IIT Varanasi, Anna University, IIT Dhanbad, NIT Surath

From your question it is added that you may not have done well in your Engineering studies. MBA is a good career switch option. You are advised to do MBA after appearing in various Entrance Examinations such as CAT, XAT, MAT, SNAP, NMAT, IIFT, IRMA, GMAT, etc.