bonerdose: this part of the .bat file is causing the issue, maybe you can review it tomorrow when you start over
# Write flash-all.bat
cat > tmp/$PRODUCT-$VERSION/flash-all.bat << EOF
@ECHO OFF
:: Copyright 2012 The Android Open Source Project
::
:: Licensed under the Apache License, Version 2.0 (the "License");
:: you may not use this file except in compliance with the License.
:: You may obtain a copy of the License at
::
::      http://www.apache.org/licenses/LICENSE-2.0
::
:: Unless required by applicable law or agreed to in writing, software
:: distributed under the License is distributed on an "AS IS" BASIS,
:: WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
:: See the License for the specific language governing permissions and
:: limitations under the License.
PATH=%PATH%;"%SYSTEMROOT%\System32"
:: Detect Fastboot version with inline PowerShell
:: Should work with Windows 7 and later
@PowerShell ^
\$version=fastboot --version; ^
try { ^
    \$verNum = \$version[0].substring(17, 6); ^
    \$verNum = \$verNum.replace('.', ''); ^
    if ((-Not (\$verNum -gt 2802)) -Or (-Not (\$verNum -match '^[\d.]+$'))) { ^
        Exit 1 ^
    } ^
} catch { ^
    Exit 1 ^
}
IF %ERRORLEVEL% NEQ 0 (
  ECHO fastboot too old; please download the latest version at https://developer.android.com/studio/releases/platform-tools.html
  EXIT /B
)