Ok, you're asking a question that only you can answer, no one here knows your style, personality, interests, etc. Too, 3-4 minutes can feel like an eternity when you're on stage . . . while experience will change this for you it's something you've not yet garnered.
Keep whatever you do simple and within your level of ability. If you are a good speaker than some form of storytelling might be effective but you must be careful to not get too wordy. Storytelling lends itself to several forms of magic such as the popular Sam the Bellhop (which would fit your time frame, but it could be a bit of a challenging bit to work out if you're not yet confident in your card work).
Stepping out and doing traditional manipulation such as Billiard Balls or Thimbles and allowing it to unfold into other such bits is another route but such an act requires time to work and develop, especially if you've not mastered the slights and techniques involved with it. But it is again, something to think about IF you have some time to develop the routine or any routine associated with classical magic such as a one-person Floating Ball sequence akin to that of Finn Jon (Ball & Cane) or Lance Burton's "Elvis" (floating bird cage) bit.
If you have some serious cash to throw at things you have Illusionetts as well as grand Illusions. The Mark Wilson & Tarbell courses both offer a nice array of easy to make big effects that require little more than cardboard, duct tape, a razor knife & paint (+ the helpers of course). A grand levitation can easily suck up that 3-4 minutes, especially something like an Asrah which can be easily made at home for less than $100.00 (IM me if this interests you). There's likewise a very inexpensive version of the Sub Trunk that can be done WITHOUT a gimmicked trunk. . . I should add that a version of this has been done by a Vegas headliner for close to 40 years now.
YOUR ASSIGNMENT: Figure out how you want to be seen by your public and what your NATURAL strengths are; you must lean on those strengths, including physical assets (I've always been known for my hair, for an example -- it's amazingly thick and has just the right amount of body that makes most women and men envy me . . . even made Franz Harary practically break down in tears one night ;-) ) If you have impediments learn how to use them as an asset. Once you can figure all that out start looking at the kinds of material you like and what, to you, fits this persona you want to project. It was pointed out in a signature that it's not the effect that's so important but rather YOU as the showman -- Peter Pit used to chew me out for "hiding behind the trick" (mostly due to my big box passion) and it is a bad habit we tend to get into; we think that this or that trick is the holy grail item that will make us famous, which is NEVER the case . . . sure, producing a car from nowhere is an excellent bit of PR but it's not what makes you "special". . . there's a reason why touring shows have to constantly reinvent themselves each season. While they always retain classic bits they are known for, they also bring in something new for the sake of generating more word of mouth chatter . . . that's how legends are created... but we're talking about the first few steps one must take when heading towards the evolution of what could be your legend.
Think about what I've said and see if that helps you. Don't go chasing the latest nifty bit of business on the market, some of the most memorable routines found in big stage shows are simple effects that have a great sense of antiquity.
Best of luck!
Also Arman where can you learn the vanishing pepsi trick?