6wks pregnant. Light bleeding 6/11, heavy 6/12, light 6/13, heavy 6/14. Cramps with heavy bleeding. HCG 356 as of 6/11, waiting for next test on 6/15. No confirmation via ultrasound as of 6/11. Is there any chance this was not a miscarriage?

HCG level today? If dropped or more or less similar, it is not a viable pregnancy.
Possible. Technically you're a threatened miscarriage and sometimes the bleeding can be heavy. Tubal pregnancy must be considered as well. Your 6/15 HCG should definitely be going up for a normal pregnancy (at least 15%-20% every 2-3 days). If dropping quickly its probably a miscarriage and if it stays almost the same, that might be an ectopic pregnancy.
You got to have. doubling of hcg in the blood every few days , if it is happening and ultrasound rules out an ectopic pregnancy then this mean your pregnancy is in good shape.