Even if marking the wrong box (the SEP IRA when you really have an SE 401k) did get you the same employer contribution, you still to the maximum employee calculation manually based on your contribution to your employer 401k, then go back to the beginning and manually input all three numbers (six on a joint return) and uncheck all the maximize boxes in all the sections, “individual” (SE) 401k AND “Keogh” (which is incorrectly called “additional” when it is the same one), without skipping it as inapplicable, to force it to accept the correct entries. Otherwise it will tell you to contribute too much and file a return with an illegally excessive refund.
