To start a finance career (IB)

Hello everyone! My name is Rodrigo and I'm getting into the finance world. I have studied Mathematics in one of the best universities of Spain and now I'm doing a Master in Banking.

My goal is to work in one of the top5 IB banks so I need some advice because I don't really have anyone near to me that can tell me nothing about this world. I don't know how to start because in the next months I should be doing an intership but I don't know where I should try to go into (within my possibilities). Should I try a consulting firm? Should I try an IB department in a small bank? Should I try to get into one of the big Investment Banks? I don´t really know where is the best place to continue my trainning and studies and where is a better place to improve my CV. I'm a little bit stressed and afraid about this because I don't want to do any mistake. I need to know what should I do next to increase my posibilities of working in a big firm in the near future. Can someone help me with this affair? 

Thank you so much,

Rodrigo