Keeping the hinge gap small isn't so much to prevent flutter but to make the controls as effective as possible. Consider the elevator...when you give up elevator you're making the whole tailplane into a cambered airfoil. There's a low pressure set up underneath compared to what's on the top surface. In effect this is what pulls the tail down which points the nose up and the model climbs. But with a large hinge gap (or any hinge gap in fact) air will bleed through the gap into the low pressure area and reduce it's effectiveness.

All you need to do is get some hinge sealing tape and put it on either the top or bottom surface to cover the gap. Your plane will fly OK as is but you'll need much larger movements of the controls than you would with the gap sealed.