Your velo has reached a level where an Ivy would be interested - but not close to the top of a recruiting class.
Your ACT is fine.
Your grades are the issue. For that to pass admissions, your HS better have an incredibly difficult curve, or have a narrative to explain the big difference between grades and scores.
If you were the absolute top tier recruit (projected future Baseball America college all-star) for a school, the coach may be able to get you through admissions; otherwise probably not. The velo doesn't put you close to the top (but it would play very well if you get there). You will know where you fit in the recruiting hierarchy by invitations for Official Visits (for the Ivies); the earlier in the semester, the better. If you are offered an OV in the first weekend, you're on the short list.
Note also, that NESCAC is D3. D3 recruiting can be brutal because of the uncertainty in getting through admissions coupled with no NLI or LL. Since you would be at the low end of the academic spectrum from many of these schools, the admissions uncertainty could play havoc with your plans.
IMO, if you get an offer from an Ivy, take it, get your completed app in the first day, keep in close touch with the coach on the special admissions committee meetings and schedule and the results once the committee meets, and keep your recruiting options going until you get word that a Likely Letter is coming. This means that your teachers need to be on board to write your LORs, the guidance counselor needs to be on board , etc. - because the app needs to be completed and submitted no later than the end of September (and that is well before most every other student and HS has geared up).
Remember, were only talking Ivy and NESCAC. Your grades, scores and velo means there are plenty of colleges which would want you. But, if you can leverage your baseball into an Ivy or NESCAC, the impact on future options could be huge. (I would not have any concerns that your HS grades are any indication of being able to succeed in an Ivy; you'll be fine once you learn how to productively study.)