Will a small mousepad mess with my aim?

Yes, if you play at low DPI / low sensitivity (like 400 DPI, 1.5 in-game), a 30x25cm pad is a recipe for frustration. Low DPI means you move your whole arm, not just your wrist, so a small pad forces constant pickups and recenters. Get something at least 45x40cm for enough space to swipe freely without hitting the edge.