advice/critic on plan for getting internship

I'm currently at a non-target state school with a 3.5 overall GPA- 3.9 in my major (finance). I have the opportunity to graduate in the fall, but I'm thinking about postponing graduation till the spring semester in order to get an investment banking internship this fall at a boutique firm. I have my first internship this summer with an insurance company. I know that selling insurance isn't really related to banking, but I figure it will make my resume look stronger and give me the summer to learn the basics of financial modeling and etc. My resume is bland right now, and I just want to give myself the summer to prepare and bolster my resume before I start cold-calling boutique banks. I know this plan isn't fool proof, but it seems like a better idea than trying to get an IB internship this summer, right?? You only get to make one first impression and I'd like to be prepared. Also, I've been studying for the GMAT to try to get into a target mfin program immediately after I graduate. Considering most mfin programs don't start until the summer or fall, delaying graduation a semester should not matter.

Thanks in advance