They make tabs with dividers between the index and middle fingers for this purpose, but most people must not like them much, because I notice that they tend to take them off the tab. Probably you should try a glove at some point to see if you like it better. However, now that you are aware of this particular problem, I would imagine you'll learn to avoid it, as long as you also learn to use back tension, which seems to be the biggest key to success in archery in general.