What is it that you're not digging in engineering? Did your exam not go as planned? If that's it, don't let one bad test dissuade you. If you're losing an actual interest in the subject, then it's time to consider switching majors. But let me say, accounting classes aren't exactly rip-roaring fun.
If you have an aptitude for the math, you might want to stick with something in that line of thinking. While accounting, investing, economics all have their charms, something in the line of physics, math, and statistics degrees would be much more marketable. Thinking along those lines, a combination of math and finance or math and economics would be a great path towards grad school. People in those fields with advanced mathematical skills are very highly prized. You can accomplish a lot in those fields with a strong understanding of calculus - total expected economic profits are found in the area between the two intersecting points of a marginal social revenue and marginal social cost functions.
Tangent to that point, if Mankato State offers the degree, a business statistics degree can be very attractive to employers. SCSU incorporates its Information Systems degree into its business college, which may be along the path you're talking about. I took a roundabout way of getting that sort of degree with an economics major and microcomputer studies minor (which I just learned that department no longer exists at SCSU, rolled into the comp. sciences section of the math department). And I would argue taking the roundabout path in school held me back the first few years out of college.